Comparative effects of cholesterol and cholesterol sulfate on hydration and ordering of dimyristoylphosphatidylcholine membranes

The comparative effect of cholesterol (CH) versus cholesterol sulfate (CS) on dimyristoylphosphatidylcholine (DMPC) membranes has been investigated by optical microscopy, freeze-fracture electron microscopy, x-ray diffraction, and solid state 2H and 31P nuclear magnetic resonance (NMR). The sulfate analogue extends the lamellar phase domain toward high water contents, and substitution of 30 mol % CH by CS in DMPC lamellae induces the trapping of 30 wt % additional water. The greater swelling of the CS-containing systems is evidenced by determination of lamellar repeat distances at maximal hydration: 147 +/- 4 A and 64 +/- 2 A in the presence of CS and CH, respectively. 2H-NMR of heavy water demonstrates that CS binds approximately 12 more water molecules at the interface than CH whereas NMR of deuterium-labeled DMPC chains reveals that 30 mol % CS orders the membrane as 15 mol % CH at high temperature and disorders much more than CH at low temperatures. The various effects of CS versus CH are discussed by taking into account attractive Van der Waals forces and repulsive steric/electrostatic interactions of the negatively charged sulfate group.

Characterization of the fluorescence emission properties of 7-azatryptophan in reverse micellar environments

The amino acid analogue 7-azatryptophan has attracted significant recent attention as a novel optical probe for protein structure, function and dynamics. We report here, for the first time, its fluorescence emission behavior in a membrane mimetic model system, namely reverse micelles of aerosol-OT in n-heptane, containing varying amounts of added H2O or D2O. Upon increase in the water/surfactant molar ratio from 0.5 to 50 the emission maximum undergoes a pronounced red shift (by 20 nm), which is accompanied by dramatic quenching of the fluorescence emission and sharp decrease in its average lifetime. These data are used to infer the microenvironments of the fluorophore in the reverse micelles. Furthermore, the highly sensitive dependence of the fluorescence emission parameters of 7-azatryptophan on the water content of the reverse micelles highlights its suitability as a probe for water restricted environments, with possible applications to interfacial regions of biomembranes.

NMR studies of DNA three-way junctions containing two unpaired thymidine bases: the influence of the sequence at the junction on the stability of the stacking conformers

DNA three-way junctions (TWJs) containing unpaired residues at the branch point can adopt a conformation in which one helix is stacked upon another, forming a coaxial, quasicontinuous double helix. As in four-way junctions (FWJs), two conformers with different stacking arrangements between the arms are possible. However, in both types of structures a markedly strong preference for one conformer has been observed. To investigate the basis for this preference, in particular the influence of the stacking proclivity of the base-pairs at the centre of the junction, two linear oligomers (36 nucleotides), TWJ1 and TWJ2, differing only in one base-pair (G.C versus C.G, respectively) at the branch point, were designed and chemically synthesized. Each one is expected to fold into a stable three-way junction, containing two unpaired thymidine bases at the junction region and two arms capped with a hairpin loop. The data obtained from 1H and 31P-NMR spectroscopy confirm that both oligomers are present as stable three-way junctions. In both TWJs two of the helical arms stack preferentially upon each other. However, the stacking arrangement is similar in both molecules. From this it is deduced that purine-purine stacking across the junction cannot be considered as a major factor that determines the preferred stacking arrangement.

Infrared and circular dichroism spectroscopic characterization of structural differences between beta-lactoglobulin A and B

Structural differences between two genetic variants of bovine beta-lactoglobulins (type A and B) in aqueous solutions were characterized using Fourier transform infrared and circular dichroism spectroscopies. To probe differences in structural dynamics, the effects hydrogen-deuterium exchange were also compared for the two proteins. The infrared spectra recorded in H2O solution for the two proteins were nearly identical in the conformationlly sensitive amide I region. The only exceptions were small differences at the band ascribed to a high-wavenumber beta-sheet component near 1693 cm-1 and the band assigned to turns at 1684 cm-1. In contrast, when the proteins were prepared in D2O solution, marked spectral differences were observed at all regions ascribed to beta-sheet and turn structures. These differences are consistent with the structural differences of the two variants at amino acid residues 64 and 118, which are located at a turn and a beta-sheet structure, respectively, as revealed by X-ray crystallographic studies [Monaco et al. (1987) J. Mol. Biol. 197, 695-706]. The circular dichroism spectra for the two proteins were essentially identical, both before and after hydrogen-deuterium exchange. Therefore, hydrogen-deuterium exchange did not alter the proteins' secondary structure. The enhancement of the amide I spectral difference upon hydrogen-deuterium exchange was ascribed to the differences in the structural mobility of the two proteins. Since the rate of exchange was greater for variant A, it was concluded that this variant has greater structural mobility than variant B. These findings indicate that the combination of infrared spectroscopy and hydrogen-deuterium exchange has great potential in characterization of even subtle structural differences in proteins induced by naturally occurring point mutations and/or site-directed mutagenesis.

Phosphorylation of glyceric acid in aqueous solution using trimetaphosphate

The phosphorylation of glyceric acid is an interesting prebiotic reaction because it converts a simple, potentially prebiotic organic molecule into phosphate derivatives that are central to carbohydrate metabolism. We find that 0.05 M glyceric acid in the presence of 0.5 M trimetaphosphate in alkaline solution gives a mixture of 2- and 3-phosphoglyceric acids in combined yields of up to 40%.

Multi-frequency bioelectrical impedance: a comparison between the Cole-Cole modelling and Hanai equations with the classical impedance index approach

Total body water and extracellular water were measured by deuterium oxide and bromide dilution respectively in 23 healthy males and 25 healthy females. In addition, total body impedance was measured at 17 frequencies, ranging from 1 kHz to 1350 kHz. Modelling programs were used to extrapolate impedance values to frequency zero (extracellular resistance) and frequency infinity (total body water resistance). Impedance indexes (height2/Zf) were computed at all 17 frequencies. The estimation errors of extracellular resistance and total body water resistance were 1% and 3%, respectively. Impedance and impedance index at low frequency were correlated with extracellular water, independent of the amount of total body water. Total body water showed the greatest correlation with impedance and impedance index at high frequencies. Extrapolated impedance values did not show a higher correlation compared to measured values. Prediction formulas from the literature applied to fixed frequencies showed the best mean and individual predictions for both extracellular water and total body water. It is concluded that, at least in healthy individuals with normal body water distribution, modelling impedance data has no advantage over impedance values measured at fixed frequencies, probably due to estimation errors in the modelled data.

Hydroxyl and water molecule orientations in trypsin: comparison to molecular dynamic structures

A comparison is presented of experimentally observed hydroxyl and water hydrogens in trypsin determined from neutron density maps with the results of a 140ps molecular dynamics (MD) simulation. Experimental determination of hydrogen and deuterium atom positions in molecules as large as proteins is a unique capability of neutron diffraction. The comparison addresses the degree to which a standard force-field approach can adequately describe the local electrostatic and van der Waals forces that determine the orientations of these hydrogens. The molecular dynamics simulation, based on the all-atom AMBER force-field, allowed free rotation of all hydroxyl groups and movement of water molecules making up a bath surrounding the protein. The neutron densities, derived from 2.1A D2O-H2O difference Fourier maps, provide a database of 27 well-ordered hydroxyl hydrogens. Virtually all of the simulated hydroxyl orientations are within a standard deviation of the experimentally-observed positions, including several examples in which both the simulation and the neutron density indicate that a hydroxyl group is shifted from a 'standard' rotamer. For the most highly ordered water molecules, the hydrogen distributions calculated from the trajectory were in good agreement with neutron density; simulated water molecules that displayed multiple hydrogen bonding networks had correspondingly broadened neutron density profiles. This comparison was facilitated by development of a method to construct a pseudo 2A density map based on the hydrogen atom distributions from the simulation. The degree of internal water molecules is shown to result primarily from the electrostatic environment surrounding that water molecule as opposed to the cavity size available to the molecule. A method is presented for comparing the discrete observations sampled in a dynamics trajectory with the time-averaged data obtained from X-ray or neutron diffraction studies. This method is particularly useful for statically-disordered water molecules, in which the average location assigned from a trajectory may represent a site of relatively low occupancy.

Assessment of total body water in paediatric patients on dialysis

BACKGROUND

Various anthropometric techniques are used to assess total body water in children on dialysis; however, their predictive accuracy and precision has not been validated.

METHODS

We compared total body water measurements obtained by deuterium oxide (D2O) dilution with predictions of total body water from (1) height and weight, (2) skinfold measurements, and (3) bioelectrical impedance analysis, using previously published formulae for healthy children. Measurements were performed in 14 patients on peritoneal and in nine patients on haemodialysis, aged 4-22 years.

RESULTS

In the total population of dialysed patients, weight was the strongest single predictor of total body water (R2 = 0.93), followed by the resistance index (RI = height2/impedance; R2 = 0.85) and height (R2 = 0.93). A prediction formula based on height and weight predicted total body water with a residual mean square error (RMSE) of 1.97 1 (coefficient of variation (CV) = 10.0%) and with a systematic overestimation of true total body water by 0.4%. A prediction equation based on skinfold measurements yielded a total body water estimate with an RMSE of 2.15 1 (CV = 10.5%) and overpredicted true total body water by an average of 2.2%. Using three published prediction equations incorporating RI, RMSEs of 2.78 1 (CV = 14.1%) with a mean under- or overestimation of true total body water by 6.9, 7.1, and 0.8% respectively, were achieved. The prediction of total body water was optimized by linear combinations of RI or the log-transformed sum of four skinfolds (logsum) with weight by the following equations: total body water (1) = 9.97 - 3.13 x logsum (1) +0.59 x weight (kg) (R2 = 0.951; RMSE = 1.67 1; CV = 8.17%). total body water (1) = 1.99 + 0.144 x RI (Ohm/cm2) (2) + 0.40 x weight (kg) (R2 = 0.949; RMSE = 1.67 1; CV = 8.53%). The fit of these prediction formulae, which were derived from the total population, did not differ significantly between haemo- and peritoneal dialysis patients or between boys and girls.

CONCLUSIONS

Both skinfold measurements and bioelectrical impedance analysis can be used to improve the height- and weight-based prediction of total body water in children on dialysis.

Neutron reflectivity studies of single lipid bilayers supported on planar substrates

Neutron reflectivity was used to probe the structure of single phosphatidylcholine (PC) lipid bilayers adsorbed onto a planar silicon surface in an aqueous environment. Fluctuations in the neutron scattering length density profiles perpendicular to the silicon/water interface were determined for different lipids as a function of the hydrocarbon chain length. The lipids were studied in both the gel and liquid crystalline phases by monitoring changes in the specularly-reflected neutron intensity as a function of temperature. Contrast variation of the neutron scattering length density was applied to both the lipid and the solvent. Scattering length density profiles were determined using both model-independent and model-dependent fitting methods. During the reflectivity measurements, a novel experimental set-up was implemented to decrease the incoherent background scattering due to the solvent. Thus, the reflectivity was measured to Q approximately 0.3 A-1, covering up to seven orders of magnitude in reflected intensity, for PC bilayers in D2O and silicon-matched (38% D2O/62% H2O) water. The kinetics of lipid adsorption at the silicon/water interface were also explored by observing changes in the reflectivity at low Q values under silicon-matched water conditions.

Energy expenditure measurements in relation to energy requirements

Long-term good health for weight-stable adults requires balance between energy intake (EI) and energy expenditure (EE). Both EI and EE measurements can be used to estimate energy requirement. Results from studies conducted at Beltsville Human Nutrition Research Center in which two or more methods were used to measure EE are compared to determine relative differences in measurement techniques. Comparison of EI estimated from dietary intake records (7 d minimum) with EI measured in 12 controlled feeding studies (45 d minimum) in 266 subjects indicated that diet records underestimate energy requirement by 18%. Comparison of EE measured in a room calorimeter and by doubly labeled water (2H(2)18O) in nine subjects showed no significant difference between methods within the calorimeter environment (1.6 +/- 2.6%) but free-living EE measured by 2H(2)18O was greater (13.2 +/- 7.1%) due to physical activity. Comparison of metabolizable energy (ME) intake, 2H(2)18O, and direct or indirect calorimetry in four subjects indicated no difference between ME and EE measured by 2H(2)18O (-1.0 +/- 1.3%) or between direct and indirect calorimetry (0.6 +/- 0.9%); however, free-living EE measured by 2H(2)18O was greater than the value calculated by calorimetry (15.3 +/- 5.0%). Each method has associated limitations that include availability, accuracy, precision, and cost. Appropriate application and interpretation of results for all methods are essential.

Evidence of histidine coordination to the catalytic ferrous ion in the ring-cleaving 2,2',3-trihydroxybiphenyl dioxygenase from the dibenzofuran-degrading bacterium Sphingomonas sp. strain RW1

The 1H NMR spectra of an aromatic ring-cleaving extradiol dioxygenase, 2,2',3-trihydroxybiphenyl dioxygenase of the dibenzofuran-degrading bacterium Sphingomonas sp. strain RW1, are reported. In the catalytically active reduced form of the monomeric enzyme (MW = 32 kDa), three broad strongly downfield shifted signals were observed, two of which disappeared in D2O solution. Their shifts and linewidths are consistent with ring NH and meta-like protons of coordinated histidines. These signals show strong sensitivity to the presence of the substrate. The oxidized form of the enzyme shows no hyperfine shifted signals. It is suggested that the high spin Fe(II) ion present in the active form of the enzyme is coordinated by at least two histidines. This is the first report of hyperfine shifted NMR signals being detected for an extradiol dioxygenase.

Multifrequency bioelectrical impedance estimates the distribution of body water

Multifrequency bioelectrical impedance analysis was used to estimate the ratio of extracellular water (ECW) to total body water in subjects with end-stage renal disease. The body's resistance was measured at frequencies ranging from 1 kHz to 1 MHz. The impedance index (height2/resistance) determined at low frequency (5 kHz) correlated most closely with ECW (r = 0.886) using sodium bromide dilution as the standard of comparison. In contrast, the ratio of height squared to resistance determined at high frequency (500 kHz) correlated most closely with total body water (r = 0.974) using deuterium oxide dilution as the standard of comparison. The ratio of resistance at 500 kHz to resistance at 5 kHz was directly correlated (r = 0.767) with the ratio of ECW to total body water. Multifrequency bioelectrical impedance analysis may assist in the evaluation of body water distribution in endstage renal disease and other clinical disorders of fluid volume and/or distribution.

Monte Carlo calculations of epithermal boron neutron capture therapy with heavy water

Much work over the past decade has centred upon the development of epithermal neutron beams for boron neutron capture therapy (BNCT) in an effort to increase thermal-neutron flux penetration and dose homogeneity throughout the brain. While heavy water has been used extensively to improve neutron penetration associated with thermal neutron beams, the effects of heavy water with epithermal neutron beams remain largely unexplored. Applying the Monte Carlo code MCNP to a heterogenous ellipsoidal skull/brain model, the effects of heavy-water replacement are studied for the JRC/ECN Petten HFR epithermal neutron beam. Thermal neutron flux and induced gamma depth dose distributions are calculated for 20% D2O replacement in comparison to standard brain and skull materials. Results are presented for both unilateral and bilateral irradiation. With bilateral irradiation, thermal-neutron flux homogeneity is substantially increased with 20% D2O replacement, thus improving the potential to give lethal doses to boron-10-loaded, disseminated cancer cells whilst avoiding local 'hot spots' to healthy tissue. Additionally, the induced gamma dose is reduced by up to 30%, substantially lowering the background dose to healthy tissue. With bilateral irradiation, 20% D2O replacement increases the therapeutic ratio from 2.25 to 2.75 for over 4 cm depth centred at the midline of the brain. These calculations use documented tumour and blood 10B concentrations for boronophenylalanine (BPA) in humans and recently documented neutron relative biological effectiveness (RBE) values.

Bacterial steroid monooxygenase catalyzing the Baeyer-Villiger oxidation of C21-ketosteroids from Rhodococcus rhodochrous: the isolation and characterization

Steroid monooxygenase from Rhodococcus rhodochrous, isolated in homogeneity with a high yield, catalyzes Baeyer-Villiger oxidation of progesterone to produce testosterone acetate with the stoichiometric consumptions of NADPH and molecular oxygen. It is a flavoenzyme with the molecular size of 60 kDa in the monomeric form and the isoelectric point of 4.9. The absorption spectrum has the maxima at 278, 376, and 439 nm and the shoulders at 360 and 465 nm, indicating a strong hypsochromic shift (blue-shift) of the absorption peak in the visible wavelength region. The prosthetic group of the enzyme was identified to be FAD, and the Kd value was estimated to be 0.95 microM. The enzyme catalyzed only the oxidative esterification of progesterone, 11 alpha- and 11 beta-hydroxyprogesterone and not the oxidative lactonization of androstenedione. Km for progesterone was 100 microM, for NADPH was 3.3 microM, and the turnover number was 185 min-1. Kd values for progesterone, 11 alpha-hydroxyprogesterone, deoxycorticosterone, and androstenedione were 110, 130, 2000, and 450 microM, respectively. The optimum pH of the reaction was about 8.5. The reaction was inhibited competitively by 17 alpha-hydroxyprogesterone and androstenedione. Amino terminal sequences of the enzymes from the bacterium and also from fungus, Cylindrocarpon radiocicola were considerably different, and the potential flavin-binding site could be detected on the amino-terminal region of the fungus enzyme but not on that of the bacterial enzyme. Western blotting analyses of the two steroid monooxygenases resulted that mouse antiserum raised for each enzyme reacted only with the antigenic enzyme protein but did not show the cross-reactions. It is clarified that bacterial steroid monooxygenase is distinctly different from the fungal enzyme in the molecular and enzymic properties.

Characterization of the structure of polydisperse human low-density lipoprotein by neutron scattering

Low-density lipoproteins (LDL) in plasma are constructed from a single molecule of apolipoprotein B-100 (M(r) 512000) in association with lipid (approximate M(r) 2-3 x 10(6)). The gross structure was studied using an updated pulsed-neutron camera LOQ with an area detector to establish the basis for the interpretation of structural changes seen during dynamic studies of LDL oxidation. Neutron-scattering data for LDL in 100% 2H2O buffers emphasize their external appearance. Guinier analysis on a continuous-flux neutron camera D17 revealed pronounced concentration-dependences in the radius of gyration, RG, and the intensity of forward scattering, I(0) (equivalent to the M(r) of LDL) between 0.5 and 11 mg of LDL protein/ml. LDL preparations from different donors gave different RG values. When extrapolated to zero concentration, RG values ranged between 8.3 and 10.6 nm and were linearly correlated with M(r), which is consistent with a spherical structure. The distance-distribution function P(r) in real space showed a single maximum at 9.1-10.9 nm, which is just under half the observed maximum dimension of 23.1 +/- 1.2 nm expected for a spherical structure. The neutron radial-density function p(r) exhibited a plateau of high and featureless density at the centre of LDL. LDL can be modelled by a polydisperse assembly of spheres with two internal densities and a mean radius close to 10.0 nm in a normal distribution of radii with a standard deviation of 2.0 nm. The data are consistent with recent electron-microscopy and ultracentrifugation data.(ABSTRACT TRUNCATED AT 250 WORDS)

Body composition of gilts at puberty

The relationship between body composition and the occurrence of puberty was evaluated using 93 Yorkshire x Landrace gilts. At approximately 60 d of age gilts were purchased and placed in a heated confinement unit where they were housed for the duration of the study. Ad libitum access to feed was provided throughout the study. Gilts were moved, mixed, and initially exposed to mature boars at approximately 120 d of age to encourage the earliest possible occurrence of puberty. Empty body weights of water, fat, protein, and ash at puberty were estimated using a deuterium dilution technique and prediction equations developed for this gilt population. There was considerable variation in age, weight, and all measures of body composition at puberty. Gilts were 138 to 240 d old and weighted 64.9 to 150.8 kg. Backfat thickness ranged from 17.5 to 44.0 mm. Gilts were composed of 32.4 to 64.3 kg of water, 15.6 to 53.9 kg of fat, 9.03 to 20.56 kg of protein, and 1.24 to 3.10 kg of ash. The coefficient of variation for fat to lean ratio at puberty was 15.39%. Linear and quadratic regressions showed that lifetime (birth to puberty) growth rate was not related to age at puberty (P > .10). Based on the variation in body composition observed it was concluded that the occurrence of puberty in gilts given ad libitum access to feed during rearing and initially exposed to mature boars at approximately 120 d of age was not related to certain minimum threshold amounts of body tissues or to a specific rate at which body tissue reserves were accumulated.

Deuterium MR in vivo imaging of the rat eye using 2H2O

In vivo deuterium MR imaging (2H MR) was investigated in rats after intraperitoneal administration of deuterated saline, and a dynamic study of the water movement in rat eyes was performed. Deuterium MR imaging was carried out by means of a gradient-echo (GRE) and a spin-echo (SE) pulse sequence. The rat eye was imaged in 2H MR more selectively by SE than by GRE, but a lower signal-to-noise ratio was obtained in 2H MR imaging using the SE sequence. The MR signal intensity of the rat eye was followed by a 3-compartment model, which enabled determination of the flow rate constant of the water in the eye (0.359/min). Deuterium MR imaging is useful to visualize the dynamic change of water in rat eyes using 2H MR at the same magnetic field (2 T) that can also be used for conventional MR imaging in humans.

Time-course studies by neutron solution scattering and biochemical assays of the aggregation of human low-density lipoprotein during Cu(2+)-induced oxidation

The oxidative modification of low-density lipoproteins (LDL) is recognized to be a key event in the development of atherosclerotic plaques on artery walls. The characteristics of LDL oxidized by cells of the artery wall can be imitated by the addition of Cu2+ ions to initiate lipid peroxidation in LDL. Neutron scattering of LDL in 2H2O buffers enables the time course of changes in the gross structure of LDL during oxidation to be continuously monitored under conditions close to physiological. Oxidation of LDL [2 mg of apolipoprotein B (apoB) protein/ml] was studied in the presence of 6.4, 25.6 and 51.2 mumol of Cu2+/g of apoB by incubation at 37 degrees C for up to 70 h. Neutron Guinier analyses showed that the radius of gyration RG (indicative of size) and the forward-scattered intensity at zero angle I(0) (indicative of M(r)) continuously increased during oxidation, indicating that LDL had aggregated. Both the rate of aggregation and the change in RG and I(0) values after 10 and 50 h increased with Cu2+ concentration. Distance-distribution functions P(r) showed that, within 4 h, the maximum dimension of LDL increased from 23 to 55 nm. The P(r) curves of oxidatively modified LDL exhibited two peaks at 10-12 nm and 26 nm. The 10-12 nm peak corresponds to native LDL, and the 26 nm peak is assigned to the initial formation of LDL dimers and trimers and their progression to form higher oligomers. The growth of the 26 nm peak depended on Cu2+ concentration. Particle-size-distribution functions Dv(r) suggested that the polydisperse spherical structure of LDL ceased to exist after 30 h, at which point the LDL samples underwent a phase separation. Related, but not identical, changes in the I(Q) and P(r) curves were observed when native LDL was self-aggregated by brief vortexing. Parallel assessment of LDL protein modification by SDS/PAGE showed increased aggregation and degradation of apoB with increased Cu2+ concentrations, and that the main apoB protein band had diminished after 2-8 h, depending on the amount of Cu2+ added. The uptake and degradation of oxidized 125I-labelled LDL by mouse peritoneal macrophages occurred maximally within the first 10 h, and increased in proportion to the Cu2+ concentration. ApoB protein broke down within the first 10 h of oxidation, and this is the period when scavenger receptors on macrophages can recognize and internalize oxidized LDL. Within 10 h, the protein-lipid interactions responsible for the spherical LDL structure became destabilized by protein fragmentation.(ABSTRACT TRUNCATED AT 400 WORDS)

Daily energy expenditure in free-living conditions in obese and non-obese children: comparison of doubly labelled water (2H2(18)O) method and heart-rate monitoring

OBJECTIVE

To compare the heart-rate monitoring with the doubly labelled water (2H2(18)O) method to estimate total daily energy expenditure in obese and non-obese children.

DESIGN

Cross sectional study of obese and normal weight children.

SUBJECTS

13 prepubertal children: six obese (4M, 2F, 9.1 +/- 1.5 years, 47.3 +/- 9.7 kg) and seven non-obese (3M, 4F, 9.3 +/- 0.6 years, 31.8 +/- 3.2 kg).

MEASUREMENTS

Total daily energy expenditure was assessed by means of the doubly labelled water method (TEEDLW) and of heart-rate monitoring (TEEHR).

RESULTS

TEEHR was significantly (P < 0.05) higher than TEEDLW in obese children (9.47 +/- 0.84 MJ/d vs 8.99 +/- 0.63 MJ/d) whereas it was not different in non-obese children (8.43 +/- 2.02 MJ/d vs 8.42 +/- 2.30 MJ/d, P = NS). The difference of TEE assessed by HR monitoring in the obese group averaged 6.2 +/- 4.7%. At the individual level, the degree of agreement (difference between TEEHR and TEEDLW +/- 2s.d.) was low both in obese (-0.36, 1.32 MJ/d) and in non-obese children (-1.30, 1.34 MJ/d). At the group level, the agreement between the two methods was good in nonobese children (95% c.i. for the bias:-0.59, 0.63 MJ/d) but not in obese children (0.04, 0.92 MJ/d). Duration of sleep and energy expenditure during resting and physical activity were not significantly different in the two groups. Patterns of heart-rate (or derived energy expenditure) during the day-time were similar in obese and non-obese children.

CONCLUSION

The HR monitoring technique provides an estimation of TEE close to that assessed by the DLW method in non-obese prepubertal children. In comparison with DLW, the HR monitoring method yields a greater TEE value in obese children.

Kt/V in CAPD by different estimations of V

This study compared the measurements of total body water (TBW) by 58% body weight (TBW58%), the Watson equation (TBWWV) and bioelectric impedance (TBWBIA) with the gold standard, Deuterium oxide (TBWD2O) dilution method in twenty continuous ambulatory peritoneal dialysis (CAPD) patients. TBW volumes were highest when calculated as TBW58% (42.6 +/- 9.4 liter) and lowest when calculated from TBWWV (34.6 +/- 6.8 liter). TBWBIA underestimated TBW when compared to TBWD2O, although the difference was not statistically significant (37.1 +/- 9.8 liter and 38.8 +/- 9.3 liter, respectively). In fact, TBWBIA correlated strongly with TBWD2O (r = 0.8, P < 0.0001). These discrepancies resulted in significant differences when Kt/V week-1 derived from the four methods were compared. To determine the effect of percent fat mass on the estimation of TBW by each method, we compared TBW and Kt/V week-1 derived from the four methods in nine CAPD patients who had normal percent fat mass (Non-Obese) and 11 CAPD patients who had greater than normal % fat mass (Obese). In the Non-Obese group, there was close correlation of TBWBIA, TBWWV and TBW58% when compared with TBWD2O (r = 0.93, P < 0.001, r = 0.89, P < 0.01 and R = 0.86, P < 0.01, respectively. Also, Kt/V week-1 derived from TBWBIA, TBWWV and TBW58% correlated strongly with Kt/V week-1 from TBWD2O (r = 0.93, P < 0.0005, r = 0.83, P < 0.01 and r = 0.8, P < 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Improved prediction formula for total body water assessment in obese women

OBJECTIVE

To validate an improved formula for the calculation of total body water (TBW) from impedance values in obese women.

SUBJECTS

A sample of 37 overweight females BMI ranging from 29.5 to 44.1 kg/m2.

MEASUREMENTS

The reference measurements for TBW were obtained by deuterium oxide dilution. Body height (h), hip circumference (C) as well as body impedance at 100 kHz (Z100) were also measured.

RESULTS

The values obtained for h, C and Z100 were introduced in the calculations and the following developed formula for total body water was determined: TBW = 0.069 [hC2/(4 pi .Z100)]+19.671. The validity of this formula was assessed through the statistical test of Bland and Altman which we also performed for other formulas containing the weight and/or the height.

CONCLUSION

We found that the accuracy of the prediction of TBW by our formula, although lower than those formulas using body weight, is higher than that which takes into account only body height. We conclude that body volume, expressed through body height and hip circumference, is a good choice of parameter in bioelectrical impedance measurements. The new approach can be useful in clinical settings for repeated monitoring of obese women, during diet-restricted treatment.

In vivo study of the biosynthesis of long-chain fatty acids using deuterated water

To determine the contributions of preexisting fatty acid, de novo synthesis, and chain elongation in long-chain fatty acid (LCFA) synthesis, the synthesis of LCFAs, palmitate (16:0), stearate (18:0), arachidate (20:0), behenate (22:0), and lignocerate (24:0), in the epidermis, liver, and spinal cord was determined using deuterated water and mass isotopomer distribution analysis in hairless mice and Sprague-Dawley rats. Animals were given 4% deuterated water for 5 days or 8 wk in their drinking water. Blood was withdrawn at the end of these times for the determination of deuterium enrichment, and the animals were killed to isolate the various tissues for lipid extraction for the determination of the mass isotopomer distributions. The mass isotopomer distributions in LCFA were incompatible with synthesis from a single pool of primer. The synthesis of palmitate, stearate, arachidate, behenate, and lignocerate followed the expected biochemical pathways for the synthesis of LCFAs. On average, three deuterium atoms were incorporated for every addition of an acetyl unit. The isotopomer distribution resulting from chain elongation and de novo synthesis can be described by the linear combination of two binomial distributions. The proportions of preexisting, chain elongation, and de novo-synthesized fatty acids as a percentage of the total fatty acids were determined using multiple linear regression analysis. Fractional synthesis was found to vary, depending on the tissue type and the fatty acid, from 47 to 87%. A substantial fraction (24-40%) of the newly synthesized molecules was derived from chain elongation of unlabeled (recycled) palmitate.

Placental norepinephrine clearance: in vivo measurement and physiological role

The intrauterine clearance rate of catecholamines is higher than in newborn animals or in adults. The separate contributions of the fetus and placenta to this clearance are not known. The placenta is a site of expression of the amine plasma membrane transporters that mediate this process. To determine the physiological role of this placental transporter in vivo, we studied fetal sheep at 123 days with common umbilical vein (UV), fetal arterial (AO), and venous catheters. Tritiated norepinephrine ([3H]NE) was infused to determine the kinetics of placental and fetal NE appearance and clearance rates. Umbilical flow was determined by [3H]NE infusion. Placental and total (fetal-placental) NE clearance rates were determined by measurement of [3H]NE from simultaneously drawn UV and AO samples. Total clearance was 99 +/- 8 ml.kg-1.min-1. Placental fractional [3H]NE extraction was 21% and accounted for 48% of total clearance. Fetal plasma NE production rate was 85 +/- 20 ng.kg-1.min-1. We conclude that placental catecholamine clearance is an important metabolic function of the placenta. This mechanism for clearance of the high fetal production rate of catecholamines is vital for fetal homeostasis. We speculate that derangements in placental catecholamine clearance may explain the exaggerated adverse effects on the fetus of drugs like cocaine, which block catecholamine transport.