Effect of Error Propagation in Stable Isotope Tracer Studies: An Approach for Estimating Impact on Apparent Biochemical Flux

Stable isotope tracers are widely used to quantify metabolic rates, and yet a limited number of studies have considered the impact of analytical error on estimates of flux. For example, when estimating the contribution of de novo lipogenesis, one typically measures a minimum of four isotope ratios, i.e., the precursor and product labeling pre- and posttracer administration. This seemingly simple problem has 1 correct solution and 80 erroneous outcomes. In this report, we outline a methodology for evaluating the effect of error propagation on apparent physiological endpoints. We demonstrate examples of how to evaluate the influence of analytical error in case studies concerning lipid and protein synthesis; we have focused on (2)H2O as a tracer and contrast different mass spectrometry platforms including GC-quadrupole-MS, GC-pyrolysis-IRMS, LC-quadrupole-MS, and high-resolution FT-ICR-MS. The method outlined herein can be used to determine how to minimize variations in the apparent biology by altering the dose and/or the type of tracer. Likewise, one can facilitate biological studies by estimating the reduction in the noise of an outcome that is expected for a given increase in the number of replicate injections.

Mechanism of skin surface lipid peroxidation

The correlation between the amount of lipid peroxide and squalene in skin surface lipid was observed by statistical analysis. To investigate the mechanism of skin surface lipid peroxidation, especially the role of active oxygen, squalene was irradiated by long wavelength ultraviolet light (UVA) with or without the photosensitizer, 8-methoxypsoralen (8MOP). Sodium azide (NaN3), a singlet oxygen quencher, or deuterium oxide, which elongates the life time of singlet oxygen, were also added in these experiments. The lipid peroxidation was detectable by observing malondialdehyde (MDA) formation. The MDA value in squalene solution was increased by UVA irradiation, and this effect was enhanced under the presence of 8MOP. These effects were repressed by the addition of NaN3 in the experimental system. These results may show that squalene peroxidation was mediated by singlet oxygen. Epidermal keratin could inhibit the increase of MDA values in human skin surface lipid in vitro. The inhibitory effect of epidermal protein on the deposition or the formation of lipid peroxide in skin surface was suggested.

Characterization of metabolically quiescent Leishmania parasites in murine lesions using heavy water labeling

Information on the growth rate and metabolism of microbial pathogens that cause long-term chronic infections is limited, reflecting the absence of suitable tools for measuring these parameters in vivo. Here, we have measured the replication and physiological state of Leishmania mexicana parasites in murine inflammatory lesions using ²H₂O labeling. Infected BALB/c mice were labeled with ²H₂O for up to 4 months, and the turnover of parasite DNA, RNA, protein and membrane lipids estimated from the rate of deuterium enrichment in constituent pentose sugars, amino acids, and fatty acids, respectively. We show that the replication rate of parasite stages in these tissues is very slow (doubling time of ~12 days), but remarkably constant throughout lesion development. Lesion parasites also exhibit markedly lower rates of RNA synthesis, protein turnover and membrane lipid synthesis than parasite stages isolated from ex vivo infected macrophages or cultured in vitro, suggesting that formation of lesions induces parasites to enter a semi-quiescent physiological state. Significantly, the determined parasite growth rate accounts for the overall increase in parasite burden indicating that parasite death and turnover of infected host cells in these lesions is minimal. We propose that the Leishmania response to lesion formation is an important adaptive strategy that minimizes macrophage activation, providing a permissive environment that supports progressive expansion of parasite burden. This labeling approach can be used to measure the dynamics of other host-microbe interactions in situ.

Microbial pathogens can adapt to changing conditions in their hosts by switching between different growth and physiological states. However, current methods for measuring microbial physiology in vivo are limited, hampering detailed dissection of host-pathogen interactions. Here we have used heavy water labeling to measure the growth rate and physiological state of Leishmania parasites in murine lesions. Based on the rate of in situ labeling of parasite DNA, RNA, protein, and lipids, we show that the growth rate of intracellular parasite stages is very slow, and that these stages enter a semi-quiescent state characterized by very low rates of RNA, protein, and membrane turnover. These changes in parasite growth and physiology are more pronounced than in in vitro differentiated parasites, suggesting that they are induced in part by the lesion environment. Despite their slow growth, the parasite burden in these lesions progressively increases as a result of low rates of parasite death and host cell turnover. We propose that these changes in Leishmania growth and physiology contribute to the development of a relatively benign tissue environment that is permissive for long term parasite expansion. This approach is suitable for studying the dynamics of other host-pathogen systems.

Under-reporting of food intake and body fatness in independent older people: a doubly labelled water study

BACKGROUND

there are no accurate methods for the assessment of food intake in older populations, under-reporting of intake being highly prevalent. There is controversy about which dietary assessment method and what person's characteristics are associated with greater under-reporting rates.

OBJECTIVE

to assess the correlation between under-reporting of energy intake (EI) and different percentages of body fat in independent older people.

DESIGN

cross-sectional study.

SETTTING

area assisted by the Family Health Program of the Ribeirão Preto Medical School, University of São Paulo, Brazil.

SUJECTS

one hundred volunteers aged 60-70 years.

METHODS

all volunteers had their body composition assessed by dual-energy x-ray absorptiometry. In second phase, 41 volunteers were evaluated, representing the four quartiles of fat percentage. Total energy expenditure (TEE) was measured by the doubly labelled water method, and EI was assessed by 24-h recalls and a food frequency questionnaire (FFQ). TEE and EI values, EI-to-TEE ratios and EI-TEE values were compared.

RESULTS

TEE was 2,220 ± 601 kcal, while the EI was 1,919 ± 602 kcal (24-h recall) and 2,119 ± 670 kcal (FFQ). The proportion of under-reporters was 31 and 40.5%, respectively. Under-reporting was more frequent in subjects with higher percentage of body fat and in females (P < 0.05).

CONCLUSION

under-reporting was more frequent among older persons with higher percentage of body fat in both methods of assessment of food intake. Older persons follow the same profile of under-reporting as younger adults.

Accuracy of a combined heart rate and motion sensor for assessing energy expenditure in free-living adults during a double-blind crossover caffeine trial using doubly labeled water as the reference method

BACKGROUND/OBJECTIVES

A combined heart rate (HR) and motion sensor (Actiheart) has been proposed as an accurate method for assessing total energy expenditure (TEE) and physical activity energy expenditure (PAEE). However, the extent to which factors such as caffeine may affect the accuracy by which the estimated HR-related PAEE contribution will affect TEE and PAEE estimates is unknown. Therefore, we examined the validity of Actiheart in estimating TEE and PAEE in free-living adults under a caffeine trial compared with doubly labeled water (DLW) as reference criterion.

SUBJECTS/METHODS

Using a double-blind crossover trial (Clinicaltrials.gov ID: #NCT01477294) with two conditions (4-day each with a 3-day-washout period), randomly ordered as caffeine (5 mg/kg per day) and placebo (malt-dextrine) intake, TEE was measured by DLW in 17 physically active men (20-38 years) who were non-caffeine users. In each condition, resting energy expenditure (REE) was assessed by indirect calorimetry and PAEE was calculated as (TEE-(REE+0.1 TEE)). Simultaneously, PAEE and TEE were estimated by Actiheart using an individual calibration (ACC+HRstep).

RESULTS

Under caffeine, ACC+HRstep explained 76 and 64% of TEE and PAEE from DLW, respectively; corresponding results for the placebo condition were 82 and 66%. No mean bias was found between ACC+HRstep and DLW for TEE (caffeine:-468 kJ per day; placebo:-407 kJ per day), although PAEE was slightly underestimated (caffeine:-856 kJ per day; placebo:-1147 kJ per day). Similar limits of agreement were observed in both conditions ranging from -2066 to 3002 and from -3488 to 1776 kJ per day for TEE and PAEE, respectively.

CONCLUSIONS

Regardless of caffeine intake, the combined HR and motion sensor is valid for estimating free-living energy expenditure in a group of healthy men but is less accurate for an individual assessment.

NMR resonance splitting of urea in stretched hydrogels: proton exchange and (1)H/(2)H isotopologues

Urea at ∼12 M in concentrated gelatin gel, that was stretched, gave (1)H and (2)H NMR spectral splitting patterns that varied in a predictable way with changes in the relative proportions of (1)H2O and (2)H2O in the medium. This required consideration of the combinatorics of the two amide groups in urea that have a total of four protonation/deuteration sites giving rise to 16 different isotopologues, if all the atoms were separately identifiable. The rate constant that characterized the exchange of the protons with water was estimated by back-transformation analysis of 2D-EXSY spectra. There was no (1)H NMR spectral evidence that the chiral gelatin medium had caused in-equivalence in the protons bonded to each amide nitrogen atom. The spectral splitting patterns in (1)H and (2)H NMR spectra were accounted for by intra-molecular scalar and dipolar interactions, and quadrupolar interactions with the electric field gradients of the gelatin matrix, respectively.

Use of H/D isotope effects to gather information about hydrogen bonding and hydrogen exchange rates

Polar side-chains in proteins play important roles in forming and maintaining three-dimensional structures, and thus participate in various biological functions. Until recently, most protein NMR studies have focused on the non-exchangeable protons of amino acid residues. The exchangeable protons attached to polar groups, such as hydroxyl (OH), sulfhydryl (SH), and amino (NH2) groups, have mostly been ignored, because in many cases these hydrogen atoms exchange too quickly with water protons, making NMR observations impractical. However, in certain environments, such as deep within the hydrophobic interior of a protein, or in a strong hydrogen bond to other polar groups or interacting ligands, the protons attached to polar groups may exhibit slow hydrogen exchange rates and thus become NMR accessible. To explore the structural and biological implications of the interactions involving polar side-chains, we have developed versatile NMR methods to detect such cases by observing the line shapes of (13)C NMR signals near the polar groups, which are affected by deuterium-proton isotope shifts in a mixture of H2O and D2O. These methods allow the detection of polar side-chains with slow hydrogen-deuterium exchange rates, and therefore provide opportunities to retrieve information about the polar side-chains, which might otherwise be overlooked by conventional NMR experiments. Future prospects of applications using deuterium-proton isotope shifts to retrieve missing structural and dynamic information of proteins are discussed.

Protein kinetic signatures of the remodeling heart following isoproterenol stimulation

Protein temporal dynamics play a critical role in time-dimensional pathophysiological processes, including the gradual cardiac remodeling that occurs in early-stage heart failure. Methods for quantitative assessments of protein kinetics are lacking, and despite knowledge gained from single-protein studies, integrative views of the coordinated behavior of multiple proteins in cardiac remodeling are scarce. Here, we developed a workflow that integrates deuterium oxide (2H2O) labeling, high-resolution mass spectrometry (MS), and custom computational methods to systematically interrogate in vivo protein turnover. Using this workflow, we characterized the in vivo turnover kinetics of 2,964 proteins in a mouse model of β-adrenergic-induced cardiac remodeling. The data provided a quantitative and longitudinal view of cardiac remodeling at the molecular level, revealing widespread kinetic regulations in calcium signaling, metabolism, proteostasis, and mitochondrial dynamics. We translated the workflow to human studies, creating a reference dataset of 496 plasma protein turnover rates from 4 healthy adults. The approach is applicable to short, minimal label enrichment and can be performed on as little as a single biopsy, thereby overcoming critical obstacles to clinical investigations. The protein turnover quantitation experiments and computational workflow described here should be widely applicable to large-scale biomolecular investigations of human disease mechanisms with a temporal perspective.

Induced radioactivity in the blood of cancer patients following Boron Neutron Capture Therapy

Since 1990, Boron Neutron Capture Therapy (BNCT) has been used for over 400 cancer patients at the Kyoto University Research Reactor Institute (KURRI). After BNCT, the patients are radioactive and their (24)Na and (38)Cl levels can be detected via a Na-I scintillation counter. This activity is predominantly due to (24)Na, which has a half-life of 14.96 h and thus remains in the body for extended time periods. Radioactive (24)Na is mainly generated from (23)Na in the target tissue that is exposed to the neutron beam in BNCT. The purpose of this study is to evaluate the relationship between the radioactivity of blood (24)Na following BNCT and the absorbed gamma ray dose in the irradiated field. To assess blood (24)Na, 1 ml of peripheral blood was collected from 30 patients immediately after the exposure, and the radioactivity of blood (24)Na was determined using a germanium counter. The activity of (24)Na in the blood correlated with the absorbed gamma ray doses in the irradiated field. For the same absorbed gamma ray dose in the irradiated field, the activity of blood (24)Na was higher in patients with neck or lung tumors than in patients with brain or skin tumors. The reasons for these findings are not readily apparent, but the difference in the blood volume and the ratio of bone to soft tissue in the irradiated field, as well as the dose that leaked through the clinical collimator, may be responsible.

Water signal attenuation by D2O infusion as a novel contrast mechanism for 1H perfusion MRI

Deuterium oxide (D2 O), which is commercially available and nonradioactive, was proposed as a perfusion tracer before the clinical usage of conventional gadolinium-based MRI contrast agents. However, the sensitivity of direct deuterium detection is the major challenge for its application. In this study, we propose a contrast-enhanced strategy to indirectly trace administered D2 O by monitoring the signal attenuation of (1) H MRI. Experiments on D2 O concentration phantoms and in vivo rat brains were conducted to prove the concept of the proposed contrast mechanism. An average maximum signal drop ratio of 5.25 ± 0.91% was detected on (1) H MR images of rat brains with 2 mL of D2 O administered per 100 g of body weight. As a diffusible tracer for perfusion, D2 O infusion is a practicable method for the assessment of tissue perfusion and has the potential to provide different information from gadolinium-based contrast agents, which have limited permeability for blood vessels. Furthermore, the observed negative relaxivities of D2 O reveal the (1) H-D exchange effect. Therefore, applications of perfusion MRI with D2 O as a contrast agent are worthy of further investigation.

Determination of steady-state protein breakdown rate in vivo by the disappearance of protein-bound tracer-labeled amino acids: a method applicable in humans

A method to determine the rate of protein breakdown in individual proteins was developed and tested in rats and confirmed in humans, using administration of deuterium oxide and incorporation of the deuterium into alanine that was subsequently incorporated into body proteins. Measurement of the fractional breakdown rate of proteins was determined from the rate of disappearance of deuterated alanine from the proteins. The rate of disappearance of deuterated alanine from the proteins was calculated using an exponential decay, giving the fractional breakdown rate (FBR) of the proteins. The applicability of this protein-specific FBR approach is suitable for human in vivo experimentation. The labeling period of deuterium oxide administration is dependent on the turnover rate of the protein of interest.

An analysis of workers' tritium concentration in urine samples as a function of time after intake at Korean pressurised heavy water reactors

In general, internal exposure from tritium at pressurised heavy water reactors (PHWRs) accounts for ∼20-40 % of the total radiation dose. Tritium usually reaches the equilibrium concentration after a few hours inside the body and is then excreted from the body with an effective half-life in the order of 10 d. In this study, tritium metabolism was reviewed using its excretion rate in urine samples of workers at Korean PHWRs. The tritium concentration in workers' urine samples was also measured as a function of time after intake. On the basis of the monitoring results, changes in the tritium concentration inside the body were then analysed.

The effect of long term calorie restriction on in vivo hepatic proteostatis: a novel combination of dynamic and quantitative proteomics

Calorie restriction (CR) promotes longevity. A prevalent mechanistic hypothesis explaining this effect suggests that protein degradation, including mitochondrial autophagy, is increased with CR, removing damaged proteins and improving cellular fitness. At steady state, increased catabolism must be balanced by increasing mitochondrial biogenesis and protein synthesis, resulting in faster protein replacement rates. To test this hypothesis, we measured replacement kinetics and relative concentrations of hundreds of proteins in vivo in long-term CR and ad libitum-fed mice using metabolic (2)H(2)O-labeling combined with the Stable Isotope Labeling in Mammals protocol and LC-MS/MS analysis of mass isotopomer abundances in tryptic peptides. CR reduced absolute synthesis and breakdown rates of almost all measured hepatic proteins and prolonged the half-lives of most (≈ 80%), particularly mitochondrial proteins (but not ribosomal subunits). Proteins with related functions exhibited coordinated changes in relative concentration and replacement rates. In silico expression pathway interrogation allowed the testing of potential regulators of altered network dynamics (e.g. peroxisome proliferator-activated receptor gamma coactivator 1-alpha). In summary, our combination of dynamic and quantitative proteomics suggests that long-term CR reduces mitochondrial biogenesis and mitophagy. Our findings contradict the theory that CR increases mitochondrial protein turnover and provide compelling evidence that cellular fitness is accompanied by reduced global protein synthetic burden.

Interaction between the ionic liquids 1-alkyl-3-methylimidazolium tetrafluoroborate and Pluronic® P103 in aqueous solution: a DLS, SANS and NMR study

The effect of three ionic liquids (ILs) 1-alkyl 3-methyl imidazlolium tetraflouroborates (C(n)mim BF(4)n=4, 6, 8) on micellar solutions of an ethylene oxide-propylene oxide block copolymer (PEO-PPO-PEO), Pluronic® P103 was examined from scattering and NMR techniques. The ILs alter the cloud point and micelle size dependant on their alkyl chain length and the results are discussed in terms of their behavior as cosolvent/cosurfactant. Cloud point data support the hydrogen bonding between the imidazolium cation and P103 while dynamic light scattering (DLS) and small angle neutron scattering (SANS) reveal that presence of ionic liquid is not conducive to the micelle formation of P103. The selective nuclear Overhauser effect (NOESY) indicates that the PPO block of the P103 interacts with the alkyl group of the C(n)mim(+) cation by hydrophobic interaction. Through this kind of interactions, C(n)mim BF(4) and P103 can form mixed micelles. This result indicates that the presence of ILs hinders the micelle formation of P103 in solution and promotes P103 to orient at air/water interface.

Isomerization of cannabidiol and Δ9-tetrahydrocannabinol during positive electrospray ionization. In-source hydrogen/deuterium exchange experiments by flow injection hybrid quadrupole-time-of-flight mass spectrometry

RATIONALE

Liquid chromatography/tandem mass spectrometry (LC/MS/MS) is frequently used for analysis of cannabinoids in drug abuse control. Despite differences in structure, the isomers Δ(9) -tetrahydrocannabinol (THC) and cannabidiol (CBD) provide identical fragment spectra after positive electrospray ionization (ESI). For elucidation of the reason, hydrogen/deuterium (H/D) exchange experiments were performed.

METHODS

Solutions of THC and CBD in D(2) O/acetonitrile (50:50, v/v) were flow-injected into acetonitrile as the mobile phase and measured by hybrid quadrupole-time-of-flight mass spectrometry (FI-QTOF-MS) in targeted MS/MS mode. The MS and collision-induced dissociation (CID) spectra at 10, 20 and 40 eV were interpreted with respect to number and position of exchanged hydrogen atoms. For comparison the same measurements were preformed in H(2) O, after addition of 0.5% formic acid and with negative ESI.

RESULTS

Depending on injected volume and position in the response curve, up to 7 or 8 hydrogen atoms were exchanged by deuterium in THC or CBD. Positive ESI CID spectra were available for precursors with up to 4 exchanged D-atoms and showed that besides the OH groups also an H/D exchange at carbon atoms of the non-aromatic part of the molecules occurred for both THC and CBD. After negative ESI, no H/D exchange in addition to the OH groups and different CID spectra of both substances was found.

CONCLUSIONS

Injection of the investigated substances in D(2) O and measurement by FI-QTOF-MS proved to be an efficient way to perform H/D exchange experiments. The results were interpreted as an acid-catalyzed in-source equilibration between THC and CBD leading to the same precursor ions and to an H/D exchange in the methyl groups under the increased acidic conditions in the positive ESI droplets. Therefore, in positive LC/ESI-MS/MS, peak identification by CID spectra or by abundance ratio of multiple reaction monitoring (MRM) transitions is not sufficient for unambiguous discrimination between THC and CBD and must be supported by retention time or other experimental evidence.

Bioelectrical impedance with different equations versus deuterium oxide dilution method for the inference of body composition in healthy older persons

BACKGROUND

There is no consensus regarding the accuracy of bioimpedance for the determination of body composition in older persons.

OBJECTIVE

This study aimed to compare the assessment of lean body mass of healthy older volunteers obtained by the deuterium dilution method (reference) with those obtained by two frequently used bioelectrical impedance formulas and one formula specifically developed for a Latin-American population.

DESIGN

A cross-sectional study.

PARTICIPANTS

Twenty one volunteers were studied, 12 women, with mean age 72±6.7 years.

SETTING

Urban community, Ribeirão Preto, Brazil.

MEASUREMENT

Fat free mass was determined, simultaneously, by the deuterium dilution method and bioelectrical impedance; results were compared. In bioelectrical impedance, body composition was calculated by the formulas of Deuremberg, Lukaski and Bolonchuck and Valencia et al.

RESULTS

Lean body mass of the studied volunteers, as determined by bioelectrical impedance was 37.8±9.2 kg by the application of the Lukaski e Bolonchuk formula, 37.4±9.3 kg (Deuremberg) and 43.2±8.9 kg (Valencia et. al.). The results were significantly correlated to those obtained by the deuterium dilution method (41.6±9.3 Kg), with r=0.963, 0.932 and 0.971, respectively. Lean body mass obtained by the Valencia formula was the most accurate.

CONCLUSION

In this study, lean body mass of older persons obtained by the bioelectrical impedance method showed good correlation with the values obtained by the deuterium dilution method. The formula of Valencia et al., developed for a Latin-American population, showed the best accuracy.

Glycerol and glycerol carbonate as ultraviscous solvents for mixture analysis by NMR

NMR of weakly polar analytes in an apolar ultraviscous solvent has recently been proposed for mixture analysis as a pertinent alternative to the DOSY experiment. The present article reports the first use of glycerol and glycerol carbonate as polar solvents for the NMR analysis of a model mixture of dipeptides. This work demonstrates the high potentiality of these solvents for the analysis of mixtures made of polar and potentially bioactive compounds. Medium-sized molecules slowly reorient in glycerol and glycerol carbonate under particular temperature conditions, so that solute resonances may show spin diffusion in NOESY spectra, thus opening the way to mixture analysis. Glycerol and glycerol carbonate have turned out to be ultraviscous solvents of choice for the individualization of four structurally close mixed dipeptides: Leu-Val, Leu-Tyr, Gly-Tyr and Ala-Tyr by means of 1D and 2D NOESY experiments. Selective sample excitation and signal detection were implemented to eliminate the intense proton signals of the non-deuterated solvents. Moreover, the recording of a multiplet selective 2D NOESY-TOCSY has shown that the analytical power of NMR in highly viscous solvents is not limited to the extraction of mixture component 1D subspectra but may also yield some supplementary information about atom connectivity within components.

Transaldolase exchange and its effects on measurements of gluconeogenesis in humans

The deuterated water method is used extensively to measure gluconeogenesis in humans. This method assumes negligible exchange of the lower three carbons of fructose 6-phsophate via transaldolase exchange since this exchange will result in enrichment of carbon 5 of glucose in the absence of net gluconeogenesis. The present studies tested this assumption. ²H₂O and acetaminophen were ingested and [1-¹³C]acetate infused in 11 nondiabetic subjects after a 16-h fast. Plasma and urinary glucuronide enrichments were measured using nuclear magnetic resonance spectroscopy before and during a 0.35 mU·kg FFM⁻¹·min⁻¹ insulin infusion. Rates of endogenous glucose production measured with [3-³H]- and [6,6-²H₂]glucose did not differ either before (14.0 ± 0.7 vs. 13.8 ± 0.7 μmol·kg⁻¹·min⁻¹) or during the clamp (10.4 ± 0.9 vs. 10.9 ± 0.7 μmol·kg⁻¹·min⁻¹), consistent with equilibration and quantitative removal of tritium during triose isomerase exchange. Plasma [3-¹³C] glucose-to-[4-¹³C]glucose and urinary [3-¹³C] glucuronide-to-[4-¹³C]glucuronide ratios were <1.0 (P < 0.001) in all subjects both before (0.66 ± 0.04 and 0.60 ± 0.04) and during (059 ± 0.05 and 0.56 ± 0.06) the insulin infusion, respectively, indicating that ∼35-45% of the labeling of the 5th carbon of glucose by deuterium was due to transaldolase exchange rather than gluconeogenesis. When corrected for transaldolase exchange, rates of gluconeogenesis were lower (P < 0.001) and glycogenolysis higher (P < 0.001) than uncorrected rates both before and during the insulin infusion. In conclusion, assuming negligible dilution by glycerol and near-complete triose isomerase equilibration, these data provide strong experimental evidence that transaldolase exchange occurs in humans, resulting in an overestimate of gluconeogenesis and an underestimate of glycogenolysis when measured with the ²H₂O method. Use of appropriate ¹³C tracers provides a means of correcting for transaldolase exchange.

Evaluation of H*(10) using the developed spherical type neutron dose monitor

An instrument for evaluating the neutron ambient dose equivalent has been developed. It has the characteristic of uniform response to wide energy of neutrons. The monitor is four-layered spherically shaped, based on moderation and absorption of neutrons. Neutron dose can be evaluated from the linear combination of three specific responses of thermoluminescent dosimeters (TLDs), which are located at three depths in the moderator. TLDs were arranged between layers of two consecutive depths on 12 radial axes at even intervals so that the monitor is equally sensitive to all directions of neutrons. In order to verify the usefulness of dose evaluation by the monitor, irradiation experiments were conducted at the FRS, JAEA. The D2O-moderated 252Cf was used for the calibration of the monitor. Experiments were also conducted by using two neutron sources of 252Cf bare and 241Am-Be. As a result, the evaluated dose for each irradiation was obtained close to the actual irradiated dose. It was confirmed that the method of dose evaluation by the developed monitor can be applied to practical neutron fields where the distance of neutron source is unknown.

Can deuterium tracing be used for reliably estimating water use of tropical trees and bamboo?

Reliable estimates of water use by trees and other woody plants are crucial for an improved understanding of plant physiology and for water resource management. Since the 1980s, the thermal dissipation probe (TDP) method has been widely applied in trees, proved to be fairly accurate but is challenging in remote areas. Also in the 1980s, the deuterium (D(2)O or deuterium oxide) tracing method was proposed, which so far has less often been applied. However, deuterium tracing requires less sophisticated equipment in the field and new analytical methods reduce costs and increase sample throughput. The objectives of this study were (i) to compare plant water use estimates of the TDP and D(2)O method and (ii) to determine whether the D(2)O method is appropriate for assessing absolute magnitudes of plant water use. The two methods were employed on five tropical tree species and a bamboo species growing in a reforestation stand in the Philippines and an agroforestry system in Indonesia. For bamboo, an increase in D(2)O values in neighbouring, non-labelled culms suggests that injected D(2)O was partly redistributed among culms, which would seriously limit the accurate estimation of water use for the target culm. For trees, water use estimates resulting from the D(2)O tracing method were proportional to the TDP results (r(2) = 0.85, P < 0.001), but absolute values were, on average, about seven times higher. This overestimation may be due to the assumptions underlying the D(2)O tracing method, such as the conservation of tracer mass, not being met. Further, it cannot be excluded that underestimation of water use by the TDP method contributed partly to the observed difference. However, when considering known sources of error, a large part of the observed difference remains unexplained. Based on our results, the use of the D(2)O tracing method cannot be recommended without further experimental testing if absolute values of whole-plant water use are a major goal. However, the D(2)O tracing method appears suitable for answering other questions, such as relative differences in water use among trees, water redistribution among neighbours and internal water transport and storage processes in plants.

Effect of crowding on the conformation of interwound DNA strands from neutron scattering measurements and Monte Carlo simulations

With a view to determining the distance between the two opposing duplexes in supercoiled DNA, we have measured small angle neutron scattering from pHSG298 plasmid (2675 base pairs) dispersed in saline solutions. Experiments were carried out under full and zero average DNA neutron scattering contrast using hydrogenated plasmid and a 1:1 mixture of hydrogenated and perdeuterated plasmid, respectively. In the condition of zero average contrast, the scattering intensity is directly proportional to the single DNA molecule scattering function (form factor), irrespective of the DNA concentration and without complications from intermolecular interference. The form factors are interpreted with Monte Carlo computer simulation. For this purpose, the many body problem of a dense DNA solution was reduced to the one of a single DNA molecule in a congested state by confinement in a cylindrical potential. It was observed that the interduplex distance decreases with increasing concentration of salt as well as plasmid. Therefore, besides ionic strength, DNA crowding is shown to be important in controlling the interwound structure and site juxtaposition of distal segments of supercoiled DNA. This first study exploiting zero average DNA contrast has been made possible by the availability of perdeuterated plasmid.

Prediction of fat-free mass by bioelectrical impedance analysis in older adults from developing countries: a cross-validation study using the deuterium dilution method

OBJECTIVE

Several limitations of published bioelectrical impedance analysis (BIA) equations have been reported. The aims were to develop in a multiethnic, elderly population a new prediction equation and cross-validate it along with some published BIA equations for estimating fat-free mass using deuterium oxide dilution as the reference method.

DESIGN AND SETTING

Cross-sectional study of elderly from five developing countries.

METHODS

Total body water (TBW) measured by deuterium dilution was used to determine fat-free mass (FFM) in 383 subjects. Anthropometric and BIA variables were also measured. Only 377 subjects were included for the analysis, randomly divided into development and cross-validation groups after stratified by gender. Stepwise model selection was used to generate the model and Bland Altman analysis was used to test agreement.

RESULTS

FFM = 2.95 - 3.89 (Gender) + 0.514 (Ht2/Z) + 0.090 (Waist) + 0.156 (Body weight). The model fit parameters were an R2, total F-Ratio, and the SEE of 0.88, 314.3, and 3.3, respectively. None of the published BIA equations met the criteria for agreement. The new BIA equation underestimated FFM by just 0.3 kg in the cross-validation sample. The mean of the difference between FFM by TBW and the new BIA equation were not significantly different; 95% of the differences were between the limits of agreement of -6.3 to 6.9 kg of FFM. There was no significant association between the mean of the differences and their averages (r= 0.008 and p= 0.2).

CONCLUSIONS

This new BIA equation offers a valid option compared with some of the current published BIA equations to estimate FFM in elderly subjects from five developing countries.

Doubly labelled water: Multi-point and two-point methods in pre-school children

OBJECTIVE

We compared the multi-sample and two-sample methods for measuring total energy expenditure (TEE) using doubly labelled water (DLW) in pre-school children to establish whether taking multiple samples provides any advantage in free-living conditions.

METHODS

Sixty-five children (32 boys; aged 2-6 years) were recruited from Aberdeen, UK. TEE was measured over 7 and 14 days using the multi-point and two-point methods by DLW. Total body composition was measured using dual-energy X-ray absorptiometry.

RESULTS

There was no significant difference between the mean TEE estimated using the multi-point and two-point methods. Independent of sampling technique, there was no significant difference in the TEE estimated over 7 and 14 days. Correlation of the deviations of the day-to-day enrichments suggests that the major factors driving isotope affected both isotopes. Association between fat-free mass (FFM) and TEE over 14 days was higher when using the multi-point method (r(2)=57.7%, P<0.001) compared with the two-point method (r(2)=41.1%, P < 0.001). There was no systematic bias in the difference between the two methods.

CONCLUSIONS

Multi- and two-point approaches give similar results for calculation of daily TEE in pre-school children. For studies aiming to establish a population level of TEE the two-sample method is a cost effective approach. However, the multi-point method appears to have greater accuracy and precision based on the better relationship to FFM (or FFM and FM combined). Consequently where maximum precision is required, in particular when energy expenditure of individual subjects is needed, this approach may be more appropriate.

Precise balancing of viscous and radiation forces on a particle in liquid-filled photonic bandgap fiber

A great challenge in microfluidics is the precise control of laser radiation forces acting on single particles or cells, while allowing monitoring of their optical and chemical properties. We show that, in the liquid-filled hollow core of a single-mode photonic crystal fiber, a micrometer-sized particle can be held stably against a fluidic counterflow using radiation pressure and can be moved to and fro (over tens of centimeters) by ramping the laser power up and down. Accurate studies of the microfluidic drag forces become possible, because the particle is trapped in the center of the single guided optical mode, resulting in highly reproducible radiation forces. The counterflowing liquid can be loaded with sequences of chemicals in precisely controlled concentrations and doses, making possible studies of single particles, vesicles, or cells.