Multipotent bone marrow cell-seeded polymeric composites drive long-term, definitive urinary bladder tissue regeneration

To date, there are no efficacious translational solutions for end-stage urinary bladder dysfunction. Current surgical strategies, including urinary diversion and bladder augmentation enterocystoplasty (BAE), utilize autologous intestinal segments (e.g. ileum) to increase bladder capacity to protect renal function. Considered the standard of care, BAE is fraught with numerous short- and long-term clinical complications. Previous clinical trials employing tissue engineering approaches for bladder tissue regeneration have also been unable to translate bench-top findings into clinical practice. Major obstacles still persist that need to be overcome in order to advance tissue-engineered products into the clinical arena. These include scaffold/bladder incongruencies, the acquisition and utility of appropriate cells for anatomic and physiologic tissue recapitulation, and the choice of an appropriate animal model for testing. In this study, we demonstrate that the elastomeric, bladder biomechanocompatible poly(1,8-octamethylene-citrate-co-octanol) (PRS; synthetic) scaffold coseeded with autologous bone marrow-derived mesenchymal stem cells and CD34+ hematopoietic stem/progenitor cells support robust long-term, functional bladder tissue regeneration within the context of a clinically relevant baboon bladder augmentation model simulating bladder trauma. Partially cystectomized baboons were independently augmented with either autologous ileum or stem-cell-seeded small-intestinal submucosa (SIS; a commercially available biological scaffold) or PRS grafts. Stem-cell synergism promoted functional trilayer bladder tissue regeneration, including whole-graft neurovascularization, in both cell-seeded grafts. However, PRS-augmented animals demonstrated fewer clinical complications and more advantageous tissue characterization metrics compared to ileum and SIS-augmented animals. Two-year study data demonstrate that PRS/stem-cell-seeded grafts drive bladder tissue regeneration and are a suitable alternative to BAE.

Effects of Anti-Inflammatory Nanofibers on Urethral Healing

Protracted postsurgical inflammation leading to postoperative complications remains a persistent problem in urethral reconstruction. Nanofibers in the form of peptide amphiphiles expressing anti-inflammatory peptides (AIF-PA) have positively modulated local inflammatory responses. Urethroplasty is performed to repair 5 mm ventral urethral defects with: uncoated small intestinal submucosa (SIS); SIS dip-coated with AIF-PA1 (anti-inflammatory treatment), or SIS dip-coated with AIF-PA6 (control) on 12-week-old male Sprague Dawley rats (n = 6/group/timepoint). Animals are euthanized at 14 and 28 d postsurgery. Hematoxylin-eosin, Masson's Trichrome, and immunohistochemistry with primary antibodies against myeloperoxidase (MPO; neutrophils), CD68, CD86, CD206 (macrophages), and proinflammatory cytokines TNFα and IL-1β are performed. Complete urethral healing occurs in 3/6 uncoated SIS (50%), 2/6 SIS+AIF-PA6 (33.3%), and 5/6 SIS+AIF-PA1 (83.3%) animals at 14 d and all at 28 d. Application of AIF-PA1 to SIS substitution urethroplasty decreases MPO⁺ neutrophils, CD86⁺ M1 proinflammatory macrophages, TNFα, and IL-1β levels while concurrently increasing levels of CD206⁺ M2 proregenerative/anti-inflammatory macrophages at the anastomoses and the regenerated tissue at the wound bed (REGEN). AIF-PA1 treatment enhances the healing process, contributing to earlier, complete urethral healing, and increased angiogenesis. Further studies are needed to elucidate the specific mechanism of inflammatory response modulation on angiogenesis and overall urethral healing.

The effects of bone marrow stem and progenitor cell seeding on urinary bladder tissue regeneration

Complications associated with urinary bladder augmentation provide the motivation to delineate alternative bladder tissue regenerative engineering strategies. We describe the results of varying the proportion of bone marrow (BM) mesenchymal stem cells (MSCs) to CD34 + hematopoietic stem/progenitor cells (HSPCs) co-seeded onto synthetic POC [poly(1,8 octamethylene citrate)] or small intestinal submucosa (SIS) scaffolds and their contribution to bladder tissue regeneration. Human BM MSCs and CD34 + HSPCs were co-seeded onto POC or SIS scaffolds at cell ratios of 50 K CD34 + HSPCs/15 K MSCs (CD34-50/MSC15); 50 K CD34 + HSPCs/30 K MSCs (CD34-50/MSC30); 100 K CD34 + HSPCs/15 K MSCs (CD34-100/MSC15); and 100 K CD34 + HSPCs/30 K MSCs (CD34-100/MSC30), in male (M/POC; M/SIS; n = 6/cell seeded scaffold) and female (F/POC; F/SIS; n = 6/cell seeded scaffold) nude rats (n = 96 total animals). Explanted scaffold/composite augmented bladder tissue underwent quantitative morphometrics following histological staining taking into account the presence (S+) or absence (S−) of bladder stones. Urodynamic studies were also performed. Regarding regenerated tissue vascularization, an upward shift was detected for some higher seeded density groups including the CD34-100/MSC30 groups [F/POC S− CD34-100/MSC30 230.5 ± 12.4; F/POC S+ CD34-100/MSC30 245.6 ± 23.4; F/SIS S+ CD34-100/MSC30 278.1; F/SIS S− CD34-100/MSC30 187.4 ± 8.1; (vessels/mm²)]. Similarly, a potential trend toward increased levels of percent muscle (≥ 45% muscle) with higher seeding densities was observed for F/POC S− [CD34-50/MSC30 48.8 ± 2.2; CD34-100/MSC15 53.9 ± 2.8; CD34-100/MSC30 50.7 ± 1.7] and for F/SIS S− [CD34-100/MSC15 47.1 ± 1.6; CD34-100/MSC30 51.2 ± 2.3]. As a potential trend, higher MSC/CD34 + HSPCs cell seeding densities generally tended to increase levels of tissue vascularization and aided with bladder muscle growth. Data suggest that increasing cell seeding density has the potential to enhance bladder tissue regeneration in our model.

The Role of Genetically Modified Mesenchymal Stem Cells in Urinary Bladder Regeneration

Recent studies have demonstrated that mesenchymal stem cells (MSCs) combined with CD34⁺ hematopoietic/stem progenitor cells (HSPCs) can function as surrogate urinary bladder cells to synergistically promote multi-faceted bladder tissue regeneration. However, the molecular pathways governing these events are unknown. The pleiotropic effects of Wnt5a and Cyr61 are known to affect aspects of hematopoiesis, angiogenesis, and muscle and nerve regeneration. Within this study, the effects of Cyr61 and Wnt5a on bladder tissue regeneration were evaluated by grafting scaffolds containing modified human bone marrow derived MSCs. These cell lines were engineered to independently over-express Wnt5a or Cyr61, or to exhibit reduced expression of Cyr61 within the context of a nude rat bladder augmentation model. At 4 weeks post-surgery, data demonstrated increased vessel number (~250 vs ~109 vessels/mm²) and bladder smooth muscle content (~42% vs ~36%) in Cyr61OX (over-expressing) vs Cyr61KD (knock-down) groups. Muscle content decreased to ~25% at 10 weeks in Cyr61KD groups. Wnt5aOX resulted in high numbers of vessels and muscle content (~206 vessels/mm² and ~51%, respectively) at 4 weeks. Over-expressing cell constructs resulted in peripheral nerve regeneration while Cyr61KD animals were devoid of peripheral nerve regeneration at 4 weeks. At 10 weeks post-grafting, peripheral nerve regeneration was at a minimal level for both Cyr61OX and Wnt5aOX cell lines. Blood vessel and bladder functionality were evident at both time-points in all animals. Results from this study indicate that MSC-based Cyr61OX and Wnt5aOX cell lines play pivotal roles with regards to increasing the levels of functional vasculature, influencing muscle regeneration, and the regeneration of peripheral nerves in a model of bladder augmentation. Wnt5aOX constructs closely approximated the outcomes previously observed with the co-transplantation of MSCs with CD34⁺ HSPCs and may be specifically targeted as an alternate means to achieve functional bladder regeneration.

Bone marrow derived cells facilitate urinary bladder regeneration by attenuating tissue inflammatory responses

Introduction

Inflammatory responses following tissue injury are essential for proper tissue regeneration. However, dysfunctional or repetitive inflammatory tissue assaults can lead to poor tissue regeneration and ultimate tissue failure via fibrosis. Previous attempts at urinary bladder tissue regeneration utilizing polymeric and biologic scaffolding materials tended to elicit these responses leading to poor tissue regeneration. Recent advances in bladder regeneration utilizing bone marrow derived mesenchymal stem cells (MSCs) and CD34⁺ hematopoietic stem/progenitor cells (HSPCs) with biocompatible citric acid based scaffolds have provided an environment that not only promotes the growth of architecturally germane and physiologically functional tissue, but also modulates aspects of the innate immune response.

Material and methods

Within this study MSCs, CD34⁺ HSPCs, or MSC/CD34⁺ HSPC seeded POC [poly (1,8-octanediol-co-citrate)] scaffolds were utilized in an established rodent bladder augmentation model to evaluate inflammation as it pertains to bladder tissue regeneration.

Results

Quantified data from post-augmentation regenerated tissue samples at the 4 week time-point demonstrated that POC/MSC and POC/MSC + CD34⁺ HSPC grafts markedly reduced the presence of pro-inflammatory CD68⁺ macrophages and MPO⁺ neutrophils compared to unseeded POC or POC/CD34⁺ HSPC-only seeded grafts. Pro-inflammatory cytokines TNFα and IL-1b were also significantly down-regulated with a concomitant increase in the anti-inflammatory cytokines IL-10 and IL-13 in the aforementioned POC/MSC and POC/MSC + CD34⁺ HSPC composites. Furthermore, this led to fewer instances of bladder tissue granuloma formation combined with greater muscle content and tissue angiogenic events as previous data has demonstrated.

Conclusions

Data indicates that POC/MSC and POC/MSC + CD34⁺ HSPC grafts attenuate the innate inflammatory response and promote bladder tissue regeneration.

The promotion of functional urinary bladder regeneration using anti-inflammatory nanofibers

Current attempts at tissue regeneration utilizing synthetic and decellularized biologic-based materials have typically been met in part by innate immune responses in the form of a robust inflammatory reaction at the site of implantation or grafting. This can ultimately lead to tissue fibrosis with direct negative impact on tissue growth, development, and function. In order to temper the innate inflammatory response, anti-inflammatory signals were incorporated through display on self-assembling peptide nanofibers to promote tissue healing and subsequent graft compliance throughout the regenerative process. Utilizing an established urinary bladder augmentation model, the highly pro-inflammatory biologic scaffold (decellularized small intestinal submucosa) was treated with anti-inflammatory peptide amphiphiles (AIF-PAs) or control peptide amphiphiles and used for augmentation. Significant regenerative advantages of the AIF-PAs were observed including potent angiogenic responses, limited tissue collagen accumulation, and the modulation of macrophage and neutrophil responses in regenerated bladder tissue. Upon further characterization, a reduction in the levels of M2 macrophages was observed, but not in M1 macrophages in control groups, while treatment groups exhibited decreased levels of M1 macrophages and stabilized levels of M2 macrophages. Pro-inflammatory cytokine production was decreased while anti-inflammatory cytokines were up-regulated in treatment groups. This resulted in far fewer incidences of tissue granuloma and bladder stone formation. Finally, functional urinary bladder testing revealed greater bladder compliance and similar capacities in groups treated with AIF-PAs. Data demonstrate that AIF-PAs can alleviate galvanic innate immune responses and provide a highly conducive regenerative milieu that may be applicable in a variety of clinical settings.

A nonhuman primate model for urinary bladder regeneration using autologous sources of bone marrow-derived mesenchymal stem cells

Animal models that have been used to examine the regenerative capacity of cell-seeded scaffolds in a urinary bladder augmentation model have ultimately translated poorly in the clinical setting. This may be due to a number of factors including cell types used for regeneration and anatomical/physiological differences between lower primate species and their human counterparts. We postulated that mesenchymal stem cells (MSCs) could provide a cell source for partial bladder regeneration in a newly described nonhuman primate bladder (baboon) augmentation model. Cell-sorted CD105(+) /CD73(+) /CD34(-) /CD45(-) baboon MSCs transduced with green fluorescent protein (GFP) were seeded onto small intestinal submucosa (SIS) scaffolds. Baboons underwent an approximate 40%-50% cystectomy followed by augmentation cystoplasty with the aforementioned scaffolds or controls and finally enveloped with omentum. Bladders from sham, unseeded SIS, and MSC/SIS scaffolds were subjected to trichrome, H&E, and immunofluorescent staining 10 weeks postaugmentation. Immunofluorescence staining for muscle markers combined with an anti-GFP antibody revealed that >90% of the cells were GFP(+) /muscle marker(+) and >70% were GFP(+) /Ki-67(+) demonstrating grafted cells were present and actively proliferating within the grafted region. Trichrome staining of MSC/SIS-augmented bladders exhibited typical bladder architecture and quantitative morphometry analyses revealed an approximate 32% and 52% muscle to collagen ratio in unseeded versus seeded animals, respectively. H&E staining revealed a lack of infiltration of inflammatory cells in grafted animals and in corresponding kidneys and ureters. Simple cystometry indicated recovery between 28% and 40% of native bladder capacity. Data demonstrate MSC/SIS composites support regeneration of bladder tissue and validate this new bladder augmentation model.

Growth factor release from a chemically modified elastomeric poly(1,8-octanediol-co-citrate) thin film promotes angiogenesis in vivo

The ultimate success of in vivo organ formation utilizing ex vivo expanded "starter" tissues relies heavily upon the level of vascularization provided by either endogenous or artificial induction of angiogenic or vasculogenic events. To facilitate proangiogenic outcomes and promote tissue growth, an elastomeric scaffold previously shown to be instrumental in the urinary bladder regenerative process was modified to release proangiogenic growth factors. Carboxylic acid groups on poly(1,8-octanediol-co-citrate) films (POCfs) were modified with heparan sulfate creating a heparan binding POCf (HBPOCf). Release of proangiogenic growth factors vascular endothelial growth factor (VEGF), fibroblast growth factor 2 (FGF2), and insulin-like growth factor 1 (IGF-1) from HBPOCfs demonstrated an approximate threefold increase over controls during a 30-day time course in vitro. Atomic force microscopy demonstrated significant topological differences between films. Subcutaneous implantation of POCf alone, HBPOCf, POCf-VEGF, and HBPOCf-VEGF within the dorsa of nude rats yielded increased vascular growth in HBPOCf-VEGF constructs. Vessel quantification studies revealed that POCfs alone contained 41.1 ± 4.1 vessels/mm², while HBPOCf, POCf-VEGF, and HBPOCF-VEGF contained 41.7 ± 2.6, 76.3 ± 9.4, and 167.72 ± 15.3 vessels/mm², respectively. Presence of increased vessel growth was demonstrated by CD31 and vWF immunostaining in HBPOCf-VEGF implanted areas. Data demonstrate that elastomeric POCfs can be chemically modified and possess the ability to promote angiogenesis in vivo.

Urinary bladder smooth muscle regeneration utilizing bone marrow derived mesenchymal stem cell seeded elastomeric poly(1,8-octanediol-co-citrate) based thin films

Bladder regeneration studies have yielded inconclusive results possibly due to the use of unfavorable cells and primitive scaffold design. We hypothesized that human mesenchymal stem cells seeded onto poly(1,8-octanediol-co-citrate) elastomeric thin films would provide a suitable milieu for partial bladder regeneration. POCfs were created by reacting citric acid with 1,8-octanediol and seeded on opposing faces with human MSCs and urothelial cells; normal bladder smooth muscle cells and UCs, or unseeded POCfs. Partial cystectomized nude rats were augmented with the aforementioned POCfs, enveloped with omentum and sacrificed at 4 and 10 weeks. Isolated bladders were subjected to Trichrome and anti-human gamma-tubulin, calponin, caldesmon, smooth muscle gamma-actin, and elastin stainings. Mechanical testing of POCfs revealed a Young's modulus of 138 kPa with elongation 137% its initial length without permanent deformation demonstrating its high uniaxial elastic potential. Trichrome and immunofluorescent staining of MSC/UC POCf augmented bladders exhibited typical bladder architecture with muscle bundle formation and the expression and retention of bladder smooth muscle contractile proteins of human derivation. Quantitative morphometry of MSC/UC samples revealed muscle/collagen ratios approximately 1.75x greater than SMC/UC controls at 10 weeks. Data demonstrate MSC seeded POCfs support partial regeneration of bladder tissue in vivo.

Defined populations of bone marrow derived mesenchymal stem and endothelial progenitor cells for bladder regeneration

PURPOSE

Autologous sources of bone marrow mesenchymal stem cells and endothelial progenitor cells are attractive alternatives to cells currently used for bladder tissue regeneration. To evaluate the potential use of these cells we determined whether mesenchymal stem cells have contractile protein profiles and physiological functions similar to those of normal bladder smooth muscle cells, and determined the angiogenic potential of endothelial progenitor cells.

MATERIALS AND METHODS

Mesenchymal stem cells and smooth muscle cells (Lonza, Gaithersburg, Maryland) underwent proliferation and Western blot analyses. Immunofluorescence imaging was performed using antibodies against smooth muscle cell epitopes. Contractility was assessed by intracellular Ca(2+) release assays and confocal microscopy after carbachol stimulation. Endothelial progenitor cells were evaluated using a chicken chorioallantoic membrane model to determine neo-angiogenic potential.

RESULTS

Western blot and immunofluorescence data showed that mesenchymal stem cells endogenously expressed known smooth muscle cell contractile proteins at levels similar to those of smooth muscle cells. Ca(2+) release assays revealed that smooth muscle cells and mesenchymal stem cells responded to carbachol treatment with a mean +/- SD of 8.6 +/- 2.5 and 5.8 +/- 0.8 RFU, respectively, which was statistically indistinguishable. Proliferation trends of mesenchymal stem cells and control smooth muscle cells were also similar. Chorioallantoic membrane assay showed the growth of vasculature derived from endothelial progenitor cells.

CONCLUSIONS

Data demonstrate that mesenchymal stem cells and smooth muscle cells express the same contractile proteins and can function similarly in vitro. Endothelial progenitor cells also have the ability to form vasculature in an in vivo chorioallantoic membrane model. These findings provide evidence that mesenchymal stem cells and endothelial progenitor cells have characteristics that may be applicable for bladder tissue regeneration.

Validity of foot-to-foot bio-electrical impedance analysis body composition estimates in overweight and obese children

OBJECTIVES: To examine the validity of body composition estimates obtained using foot-to-foot bio-electrical impedance analysis (BIA) in overweight and obese children by comparison to a reference four-compartment model (4-CM). SUBJECTS/METHODS: 38 males: age (mean +/- sd) 13.6 +/- 1.3 years, body mass index 30.3 +/- 6.0 kg.m(-2) and 14 females: age 14.7 +/- 2.2 years, body mass index 32.4 +/- 5.7 kg.m(-2) participated in the study. Estimates of fat-free mass (FFM), fat mass (FM) and percentage body fat (PBF) obtained using a Tanita model TBF-310 and a 4-CM (derived from body mass, body volume, total body water and total body bone mineral measurements) were compared using bias and 95% limits of agreement (Tanita minus 4-CM estimates). RESULTS: Body composition estimates obtained with the Tanita TBF-310 were not significantly different from 4-CM assessments: for all subjects combined the bias was -0.7kg for FM, 0.7kg for FFM and -1.3% for PBF. However, the 95% limits of agreement were substantial for individual children: males, up to +/-9.3kg for FFM and FM and +/-11.0% for PBF; females, up to +/-5.5kg for FFM and FM and +/-6.5% for PBF. CONCLUSIONS: The Tanita TBF-310 foot-to-foot BIA body composition analyser with the manufacturer's prediction equations is not recommended for application to individual children who are overweight and obese although it may be of use for obtaining group mean values.

Composition of the fat-free mass in obese and nonobese children: matched case-control analyses

OBJECTIVE

Most body composition techniques assume constant properties of the fat-free mass (FFM), such as hydration, density and mineralisation. Previous studies suggested that FFM composition may change in childhood obesity; however, this issue has not been investigated in detail.

AIM

To compare FFM composition in obese and nonobese children.

DESIGN

Observational matched case-control analyses.

SUBJECTS

A total of 28 obese children (13 boys, 15 girls) and 22 nonobese children (10 boys, 12 girls) aged 7-14 y. Obesity was defined as body mass index centile >95.

METHODS

Measurements were made of weight, height, total body water, and body volume. Bone mineral content was estimated in a subsample. Body composition was calculated using three- and four-component models.

RESULTS

According to the three-component model (n=22 matched pairs), obese children had greater hydration (P<0.05), and reduced density (P=0.057) of FFM. According to the four component model (n=11 pairs), obese children had greater hydration (P<0.01) and reduced density (P<0.002) of FFM. The mineralisation of FFM was increased, but not significantly so.

CONCLUSION

The greater hydration and reduced density of FFM of obese children should be taken into account if body composition is to be measured with optimum accuracy during treatment programmes. These differences may be addressed by using multicomponent rather than two-component models of body composition. Although the greater mineralisation of FFM in obese children was not significant in the present study, the four-component model is best able to address the combined differences in hydration and mineralisation that occur in childhood obesity.

Use of a reference four-component model to define the effects of insulin treatment on body composition in type 2 diabetes: the 'Darwin study'

AIMS

To define the effects of insulin treatment on body composition and fat distribution, and investigate the potential role of body weight (BWt) gain predictors in patients with poorly controlled type 2 diabetes.

METHODS

Assessments of body composition, using a four-component model, and biochemical indices were obtained in 19 patients [mean (SD): age, 60 (8.3) years; BMI, 25.3 (3.3) kg/m(2)] with poorly controlled type 2 diabetes, despite maximal oral hypoglycaemic agents, receiving insulin [40 (12.2) units/day] at baseline and after 1, 3 and 6 months.

RESULTS

Insulin therapy significantly reduced plasma glucose [-6.0 (4.3) mmol/l], improved [HbA(1)c [-1.9 (1.8)%], and reversed the BWt lost [3.3 (1.8) kg] before treatment. The 6-month BWt gain [+5.2 (2.7) kg] consisted of body fat [+2.9 (2.7) kg] and fat-free mass [FFM; +2.3 (1.8) kg], with the FFM increase due solely to total body water [TBW; +2.4 (1.5) l], as there were no detectable changes in total body protein or bone mineral, thereby increasing FFM hydration by 1.3%. More body fat was deposited centrally in patients receiving insulin alone than those receiving insulin with an oral hypoglycaemic agent (metformin). Daily insulin dose, HbA(1)c and hip circumference were independent predictors of BWt gain.

CONCLUSIONS

Insulin treatment increased fat and FFM similarly in poorly controlled type 2 diabetes patients, with the FFM gain due entirely to TBW. The possible role of metformin in reducing central fat accumulation following insulin treatment warrants further investigation into its mechanism and potential long-term benefits.

Within- and between-laboratory precision in the measurement of body volume using air displacement plethysmography and its effect on body composition assessment

OBJECTIVE

To determine and compare the extent of within- and between-laboratory precision in body volume (BV) measurements using air displacement plethysmography (ADP), the BOD POD body composition system, and to interpret any such variability in terms of body composition estimates.

DESIGN

Repeated test procedures of BV assessment using the BOD POD ADP were reproduced at two laboratories for the estimation of precision, both within and between laboratories.

SUBJECTS

In total, 30 healthy adult volunteers, 14 men (age, 19-48 y; body mass index (BMI), 19.7-30.3 kg/m2) and 16 women (age, 19-40 y; BMI, 16.3-35.7 kg/m2), were each subjected to two test procedures at both laboratories. Two additional volunteers were independently subjected to 10 repeated test procedures at both laboratories.

MEASUREMENTS

Repeated measurements of BV, uncorrected for the effects of isothermal air in the lungs and the surface area artifact, were obtained using the BOD POD ADP, with the identical protocol being faithfully applied at both laboratories. Uncorrected BV measurements were adjusted to give estimates of actual BV that were used to calculate body density (body weight (BWt)/actual BV) from which estimates of body composition were derived. The differences between repeated BV measurements or body composition estimates were used to assess within-laboratory precision (repeatability), as standard deviation (SD) and coefficient of variation; the differences between measurements reproduced at each laboratory were used to determine between-laboratory precision (reproducibility), as bias and 95% limits of agreement (from SD of the differences between laboratories).

RESULTS

The extent of within-laboratory methodological precision for BV (uncorrected and actual) was variable according to subject, sample group and laboratory conditions (range of SD, 0.04-0.13 l), and was mostly due to within-individual biological variability (typically 78-99%) rather than to technical imprecision. There was a significant (P<0.05) bias between laboratories for the 10 repeats on the two independent subjects (up to 0.29 l). Although no significant bias (P=0.077) was evident for the sample group of 30 volunteers (-0.05 l), the 95% limits of agreement were considerable (-0.68 to 0.58 l). The effects of this variability in BV on body composition were relatively greater: for example, within-laboratory precision (SD) for body fat as % BWt was between 0.56 and 1.34% depending on the subject and laboratory; the bias (-0.59%) was not significant between laboratories, but there were large 95% limits of agreement (-3.67 to 2.50%).

CONCLUSION

Within-laboratory precision for each BOD POD instrument was reasonably good, but was variable according to the prevailing conditions. Although the bias between the two instruments was not significant for the BV measurements, implying that they can be used interchangeably for groups of similar subjects, the relatively large 95% limits of agreement indicate that greater consideration may be needed for assessing individuals with different ADP instruments. Therefore, use of a single ADP instrument is apparently preferable when assessing individuals on a longitudinal basis.

Evaluation of air-displacement plethysmography in children aged 5-7 years using a three-component model of body composition

The aim of the present study was to evaluate air-displacement plethysmography (ADP) in children aged 5-7 years. Body-composition measurements were obtained by ADP, (2)H dilution and anthropometry in twenty-eight children. Calculation of body volume by ADP was undertaken using adult and children's equations for predicting lung volume and surface area. Fat-free mass (FFM) was calculated using a three-component model. Measured FFM hydration was then compared with values from the reference child. Differences between measured and reference hydration were back-extrapolated, to calculate the error in ADP that would account for any disagreement. Propagation of error was used to distinguish the contributions of methodological precision and biological variability to total hydration variability. The use of children's equations influenced the results for lung volume but not surface area. The mean difference between measured and reference hydration was 0.6 (sd 1.7) % (P<0.10), equivalent to an error in body volume of 0.04 (sd 0.20) litres (P<0.30), and in percentage fat of 0.4 (sd 1.9) (P<0.28). The limits of agreement in individuals could be attributed to methodological precision and biological variability in hydration. It is concluded that accuracy of ADP was high for the whole group, with a mean bias of <0.5 % fat using the three-component model, and after taking into account biological variability in hydration, the limits of agreement were around +/-2 % fat in individuals. Paediatric rather than adult equations for lung volume estimation should be used.

Segmental bioelectrical impedance analysis in children aged 8-12 y: 2. The assessment of regional body composition and muscle mass

OBJECTIVES

To investigate the potential of segmental bioelectrical impedance analysis (BIA) for assessing regional composition and muscle mass in children.

DESIGN

Strengths of relationships were determined between (a) BIA indices of trunk, limbs or limb segments and (b) segment fat or fat-free mass (FFM) assessed using dual-energy X-ray absorptiometry (DXA); the extent of agreement was established between two independent models, based on DXA and BIA, of limb muscle and adipose tissue (AT) mass.

SUBJECTS

Eighteen boys and 19 girls aged 8-12 y.

MEASUREMENTS

BIA and anthropometry of trunk, whole limbs, limb segments and defined sections were used to calculate segmental impedance indices and specific resistivities; segment fat and FFM were obtained using DXA; muscle and AT masses of limbs, segments and sections were estimated using DXA and BIA models, and by anthropometry.

RESULTS

Segmental BIA indices were significantly related to composition of the segments assessed using DXA; although substantial bias was observed, there was fairly good agreement (low 95% limits of agreement) between the BIA and DXA models of muscle mass and estimates from each were similarly categorised in tertiles, as were estimates of AT.

CONCLUSION

Segmental BIA appears to have potential for assessing in children the composition of body segments, as obtained using DXA, and the masses of muscle and AT in whole limbs, limb segments and defined sections.

Segmental bioelectrical impedance analysis in children aged 8-12 y: 1. The assessment of whole-body composition

OBJECTIVES

To investigate the potential of segmental bioelectrical impedance analysis (BIA) for estimating whole-body composition in children.

DESIGN

Strengths of relationships were determined between indices of impedance or specific resistivities of body segments and reference four-component model (4-CM) assessments of body composition.

SUBJECTS

Eighteen boys and 19 girls aged 8-12 y.

MEASUREMENTS

Whole-body and segment BIA and anthropometry were used to calculate impedance indices of the whole body and segments and specific resistivities of segments; total body water (TBW), fat-free mass (FFM) and body fat were assessed using the 4-CM.

RESULTS

Segmental BIA indices were significantly related to body composition, provided that appropriate comparisons were undertaken for each index: impedance adjusted for unit segment length was better related to TBW and FFM, whereas segment specific resistivity was better related to body fat. Differences between body composition estimates obtained with the 4-CM and predicted using BIA were partly dependent on limb-to-trunk ratios of BIA indices.

CONCLUSION

Segmental BIA has potential for providing additional alternative approaches to the assessment of whole-body composition in children: (a) FFM and TBW were best related to impedance adjusted for segment length; (b) body fat was best related to segment specific resistivity; and (c) the relative influences of different segment BIA indices may be utilisable for generating more valid whole-body composition estimates.

The potential of near infra-red interactance for predicting body composition in children

OBJECTIVE

To establish whether near infra-red interactance (NIRI) has potential for use instead of skinfold thickness (SFT) measurements in the assessment of body composition in young children.

DESIGN

Strengths of relationships were established between NIRI or SFT measurements and four-component model (4-CM) assessments of body composition.

SUBJECTS

Nineteen boys and 19 girls, aged 8-12 y.

MEASUREMENTS

4-CM estimates of body composition were obtained from measurements of body weight, body volume, bone mineral content and total body water. SFT and NIRI were measured at the same four recognized sites (biceps, triceps, subscapular and suprailiac).

RESULTS

All children subjectively expressed a preference for NIRI rather than SFT calipers. Although SFTs were slightly more strongly and consistently related to 4-CM estimates, NIRI measurements at the biceps, subscapular and sum of four sites were significantly related to body composition indices. Subscapular NIRI measurements were as successful as subscapular SFTs in ranking subjects relative to 4-CM fatness, both techniques being most successful at lower levels of fatness.

CONCLUSION

NIRI has potential for use instead of SFT for estimating body composition in young children. Its contribution may prove to be greatest in sick children in whom SFT measurements may be unwelcome, and weight-for-height indices of little value due to abnormalities of water distribution. However, greater numbers are required to develop child-specific prediction equations and the viability and validity of NIRI in pediatric patients is still to be evaluated.

Precision of measurement and body size in whole-body air-displacement plethysmography

OBJECTIVE

To investigate methodological and biological precision for air-displacement plethysmography (ADP) across a wide range of body size.

DESIGN

Repeated measurements of body volume (BV) and body weight (WT), and derived estimates of density (BD) and indices of fat mass (FM) and fat-free mass (FFM).

SUBJECTS

Sixteen men, aged 22--48 y; 12 women, aged 24--42 y; 13 boys, aged 5--14 y; 17 girls, aged 5--16 y.

MEASUREMENTS

BV and WT were measured using the Bodpod ADP system from which estimates of BD, FM and FFM were derived. FM and FFM were further adjusted for height to give fat mass index (FMI) and fat-free mass index (FFMI).

RESULTS

ADP is very precise for measuring both BV and BD (between 0.16 and 0.44% of the mean). After removing two outliers from the database, and converting BD to body composition, precision of FMI was <6% in adults and within 8% in children, while precision of FFMI was within 1.5% for both age groups.

CONCLUSION

ADP shows good precision for BV and BD across a wide range of body size, subject to biological artefacts. If aberrant values can be identified and rejected, precision of body composition is also good. Aberrant values can be identified by using pairs of ADP procedures, allowing the rejection of data where successive BD values differed by >0.007 kg/l. Precision of FMI obtained using pairs of procedures improves to <4.5% in adults and <5.5% in children.

Evaluation of a model for total body protein mass based on dual-energy X-ray absorptiometry: comparison with a reference four-component model

The aim of the present study was to evaluate a model of body composition for assessing total body protein (TBP) mass using dual-energy X-ray absorptiometry (DXA), with either measured or assumed total body water (TBW); it was intended to provide a less complex or demanding alternative technique to, for example, the four-component model (4-CM). The following measurements were obtained in healthy adults (n 46) aged 18--62 years, and children (n 30) aged 8--12 years: body weight (BWt), body volume (BV; under-water weighing), TBW ((2)H-dilution space or predicted using an assumed hydration fraction of fat-free mass (HF(ffm))), bone mineral content (BMC; DXA) and fat-free soft tissue (FFST; DXA). TBP was calculated using the 4-CM (TBP = 3.05BWt -- 0.290TBW -- 2.734BMC -- 2.74BV) and the DXA model (TBP = FFST -- 0.2302BMC -- TBW). DXA measurements were obtained using the Lunar DPX (Lunar Radiation Corporation, Madison, WI, USA) or Hologic QDR 1000/W (Hologic, Waltham, MA, USA). Precision of the DXA model for TBP with measured TBW (4.6--6.8 % mean TBP) was slightly worse than the 4-CM (4.0--5.4 %), whereas that modelled with assumed HF(ffm) was more precise (2.4--5.2 %) because it obviated imprecision associated with measuring TBW. Agreement between the 4-CM and DXA model with measured TBW was also worse (e.g. bias, 15 % of the mean; 95 % limits of agreement up to +/-39 % for adults measured on the Lunar DPX) than when a constant for HF(ffm) was assumed (3.7 % and +/-21 % respectively). Most of the variability in agreement between these various models was due to interpretation of biological factors, rather than to measurement imprecision. Therefore, the DXA model, which is less complex and demanding than the 4-CM, is of value for assessing TBP in groups of healthy subjects, but is of less value for individuals in whom there may be substantial differences from reference 4-CM estimates.

Comparison of recoveries in breath carbon dioxide of H13CO-3 and H14CO-3 administered simultaneously by single 6 h constant unprimed intravenous infusion

The aim of this study was to assess the bioequivalence of H13CO-3 and H14CO-3, by administering both labels simultaneously by single infusion and comparing their recovery in breath CO2 and urinary urea. Six healthy male subjects (age range 24-41 years; weight 76.7 (sd, 18.6) kg; height 1.79 (sd 0.05) m) were infused with unprimed solutions of HCO3- (110.0 mmol/kg) labelled with 13C (0.76 mmol 13C/h) and 14C (48 Bq/h) at a constant rate for 6 h, in a whole-body calorimeter (1400 litres) for measurement of CO2 production. Samples of breath were collected hourly in a Douglas bag and all urine was collected into two batches (0-4 h and 4-6 h) for estimating recovery of infused label by measurement of enrichment or specific activity. Recovery in breath CO2 of both labels increased from about 25 % for the first hour to 88 % and above for hours 3-4 onwards. Mean recovery of 13C in breath CO2 was slightly higher than that of 14C for all periods (mean difference always less than 1 % of infused label) but was significant only for the first 3 h (P < 0.05). Recovery of 14C in urea was significantly higher (P < 0.01) than 13C, but was confounded by substantial variability and uncertainties concerning 13CO2 background enrichments. These results suggest that there is no compelling need to alter factors currently used for recovery of 14C in breath when using 13C instead, and vice versa.

Modeling leg sections by bioelectrical impedance analysis, dual-energy X-ray absorptiometry, and anthropometry: assessing segmental muscle volume using magnetic resonance imaging as a reference

This study aimed to assess the value of different DXA and BIA models for predicting muscle volume in mid-thigh segments obtained by MRI. Three DXA models were used: in model A, muscle was taken to be equivalent to fat-free soft tissue; in model B the thigh segment was divided into its constituent tissues using fixed assumptions about tissue composition; in model C the assumptions were similar to model B, but with variable distribution of fat and fat-free soft tissue, depending on body mass index. The two BIA models (both parallel tissue resistance models) involved impedance measurements at 50 kHz, and assumptions about either the specific resistivities of all the constituent tissues (model A), or resistivities of only adipose tissue and muscle (model B). Anthropometric estimates (thigh circumference and skinfold thickness) assumed that both limb and muscle circumference were circular. Compared to MRI estimates of muscle mass, those obtained by DXA model A (fat-free soft tissue) were not as good as those obtained using models B and C, although the standard deviations of the differences were similar with all three models. The BIA models were superior to the anthropometric estimates of muscle volume (relative to MRI) with respect to bias, but the standard deviations of the differences were large for both. The intraobserver repeatabilities for muscle volume were < 0.5% for MRI, < 1% for DXA, 1.8% for BIA, and 1.7% for anthropometry (interobserver value for BIA was 3.8% and for anthropometry 3.5%). The study suggests that DXA modeling provides a promising approach for assessing muscle mass in thigh segments, and suggests the potential value of parallel BIA models for groups of individuals but not for individual subjects, possibly because muscle resistivity is influenced not only by its composition but also by the direction of current flow in muscle.

Assessment of body volume using three-dimensional photonic scanning

Measurement of body volume (BV) can be used to estimate body composition using two- or multicomponent models. The traditional approach, underwater weighing (UWW), is awkward and unsuitable for many subjects. A newer alternative, whole body air displacement plethysmography (ADP), is less demanding but still unsuitable for young children, who may not remain still during the measurement. We have, therefore, considered whether a novel approach, three-dimensional photonic scanning, is a viable alternative. Duplicate measurements of body volume were obtained in 22 adults (11 of each sex; mean [SD] BMI, 21.8 [2.5] kg/m2) by UWW, ADP, and a Hamamatsu Bodyline Scanner (HBS) (Hamamatsu, Japan). Subjects wore a tight-fitting swimming costume for all three measurements, which were performed within one day of each other. Scans lasted 10 seconds, with the subject standing in a predefined position. The body surface skin was reconstructed using a B-spline-fitting model. In UWW, lung volume (LV) was measured simultaneously with underwater weight. In ADP and HBS, LV was predicted from weight and height. Results were compared using correlation and Bland and Altman analysis. Correlation analysis indicated that the scanner successfully ranked subjects in terms of BV. However, Bland and Altman analysis demonstrated that, relative to both UWW and ADP, HBS measured BV without bias but with limits of agreement between individuals of > 2 liters, equivalent to approximately 20% fat. Scan precision was 0.57 liter, or 4.1% fat. Although HBS cannot yet measure BV with sufficient accuracy to predict fatness, much of the error is probably due to difficulties in standardizing LV during the scan. Simultaneous measurement of LV with volume by HBS is expected to improve limits of agreement substantially. Occlusion is also an important source of error. The method offers many advantages over alternative techniques, because the measurement is brief, noninvasive, and suitable for repeat measurements.

Whole body air displacement plethysmography compared with hydrodensitometry for body composition analysis

AIMS

To assess the acceptability and feasibility of whole body air displacement plethysmography in children and to determine its precision and agreement with hydrodensitometry, an appropriate reference method.

METHODS

Age specific two component model equations were used to predict fat mass from body density in 22 children aged 8-12 years and in 10 adults for comparison of methods. Precision for each method was established from duplicate measurements.

RESULTS

Plethysmography was accepted more readily than hydrodensitometry (100% v 69% provided duplicate measurements). Precision for fat mass in children was 0.38 kg by plethysmography and 0.68 kg by hydrodensitometry, and results were similar in adults. The mean (SD) fat mass in children was 6.9 kg (4.0) and 6.7 kg (4. 2) by plethysmography and hydrodensitometry, respectively, but 95% limits of agreement between methods were large (-4.1 kg to 3.5 kg fat).

CONCLUSION

Plethysmography was more readily accepted and had better precision than hydrodensitometry. It also provided similar body composition results for the group but not for all individual children.

Assessment of limb muscle and adipose tissue by dual-energy X-ray absorptiometry using magnetic resonance imaging for comparison

OBJECTIVE

To use magnetic resonance imaging (MRI) to validate estimates of muscle and adipose tissue (AT) in lower limb sections obtained by dual-energy X-ray absorptiometry (DXA) modelling.

DESIGN

MRI measurements were used as reference for validating limb muscle and AT estimates obtained by DXA models that assume fat-free soft tissue (FFST) comprised mainly muscle: model A accounted for bone hydration only; model B also applied constants for FFST in bone and skin and fat in muscle and AT; model C was as model B but allowing for variable fat in muscle and AT.

SUBJECTS

Healthy men (n = 8) and women (n = 8), ages 41-62y; mean (s.d.) body mass indices (BMIs) of 28.6 (5.4) kg/m2 and 25.1 (5.4) kg/m2, respectively.

MEASUREMENTS

MRI scans of the legs and whole body DXA scans were analysed for muscle and AT content of thigh (20 cm) and lower leg (10 cm) sections; 24h creatinine excretion was measured.

RESULTS

Model A overestimated thigh muscle volume (MRI mean, 2.3 l) substantially (bias 0.36 l), whereas model B underestimated it by only 2% (bias 0.045 l). Lower leg muscle (MRI mean, 0.6 l) was better predicted using model A (bias 0.04 l, 7% overestimate) than model B (bias 0.1 l, 17% underestimate). The 95% limits of agreement were high for these models (thigh, +/-20%; lower leg, +/-47%). Model C predictions were more discrepant than those of model B. There was generally less agreement between MRI and all DXA models for AT. Measurement variability was generally less for DXA measurements of FFST (coefficient of variation 0.7-1.8%) and fat (0.8-3.3%) than model B estimates of muscle (0.5-2.6%) and AT (3.3-6.8%), respectively. Despite strong relationships between them, muscle mass was overestimated by creatinine excretion with highly variable predictability.

CONCLUSION

This study has shown the value of DXA models for assessment of muscle and AT in leg sections, but suggests the need to re-evaluate some of the assumptions upon which they are based.

Predicting composition of leg sections with anthropometry and bioelectrical impedance analysis, using magnetic resonance imaging as reference

Magnetic resonance imaging (MRI) was used to evaluate and compare with anthropometry a fundamental bioelectrical impedance analysis (BIA) method for predicting muscle and adipose tissue composition in the lower limb. Healthy volunteers (eight men and eight women), aged 41 to 62 years, with mean (S.D.) body mass indices of 28.6 (5.4) kg/m2 and 25.1 (5.4) kg/m2 respectively, were subjected to MRI leg scans, from which 20-cm sections of thigh and 10-cm sections of lower leg (calf) were analysed for muscle and adipose tissue content, using specifically developed software. Muscle and adipose tissue were also predicted from anthropometric measurements of circumferences and skinfold thicknesses, and by use of fundamental BIA equations involving section impedance at 50 kHz and tissue-specific resistivities. Anthropometric assessments of circumferences, cross-sectional areas and volumes for total constituent tissues matched closely MRI estimates. Muscle volume was substantially overestimated (bias: thigh, -40%; calf, -18%) and adipose tissue underestimated (bias: thigh, 43%; calf, 8%) by anthropometry, in contrast to generally better predictions by the fundamental BIA approach for muscle (bias: thigh, -12%; calf, 5%) and adipose tissue (bias: thigh, 17%; calf, -28%). However, both methods demonstrated considerable individual variability (95% limits of agreement 20-77%). In general, there was similar reproducibility for anthropometric and fundamental BIA methods in the thigh (inter-observer residual coefficient of variation for muscle 3.5% versus 3.8%), but the latter was better in the calf (inter-observer residual coefficient of variation for muscle 8.2% versus 4.5%). This study suggests that the fundamental BIA method has advantages over anthropometry for measuring lower limb tissue composition in healthy individuals.

Four-component model of body composition in children: density and hydration of fat-free mass and comparison with simpler models

BACKGROUND

Body composition in children is generally measured by 2-component (2C) models, which are subject to error arising from variation in fat-free mass (FFM) composition. The 4-component (4C) model, which divides body weight into fat, water, mineral, and protein, can overcome these limitations.

OBJECTIVE

The aims of our study were to 1) describe 4C model data for children aged 8-12 y; 2) evaluate interindividual variability in the hydration, bone mineral content, and density of FFM; 3) evaluate the success with which 2C models and bedside techniques measure body composition in this age group with use of the 4C model as a reference.

DESIGN

Dual-energy X-ray absorptiometry, underwater weighing, deuterium dilution, bioelectrical impedance analysis, and anthropometry were used to determine body composition in 30 children. The contribution of methodologic error to the observed variability in the hydration and density of FFM was evaluated by using propagation of error.

RESULTS

Mean (+/-SD) FFM density and hydration were 1.0864+/-0.0074 kg/L and 75.3+/-2.2%, respectively, and were significantly different from adult values (P < 0.02). Relative to the 4C model, deuterium dilution and dual-energy X-ray absorptiometry showed no mean bias for fatness, whereas underwater weighing underestimated fatness (P < 0.025). Fatness determined by using skinfold-thickness and bioelectrical impedance analysis measurements along with published equations showed poor agreement with 4C model data.

CONCLUSIONS

Biological variability and methodologic error contribute equally to the variability of FFM composition. Our findings have major implications for bedside prediction methods used for children, traditionally developed in relation to underwater weighing.

Precision and accuracy in a metabolic monitor for indirect calorimetry

OBJECTIVE

To determine within-machine and between-machine precision (reproducibility) and accuracy, of the Deltatrac Mk 1 Metabolic Monitor.

DESIGN

Within-machine and between-machine comparison for gas exchange (VO2 and VCO2), respiratory quotient (RQ) and energy expenditure (EE).

SUBJECTS

3 Deltatrac Mk 1 Metabolic Monitors.

METHODS

Within-machine and between-machine reproducibility were assessed by five successive 10 min gas infusion tests in each machine. Accuracy was assessed by measuring independently the gas content of the infusion mixture. The Deltatrac flowmeters were evaluated by further infusion tests.

RESULTS

Within-study reproducibility was < 1 ml/min for VCO2, < 2.5 ml/min for VO2, < 5 kcal/d for EE and < 0.01 for RQ. Between-study reproducibility was < 0.2% for RQ, < 1% for VCO2 and < 2% for VO2 and EE. Between-machine reproducibility was < 0.1% for RQ and < 1% for VO2, VCO2 and EE. Accuracy in all three machines was within 3% for VO2, VCO2 and EE, and within 0.2% for RQ.

CONCLUSIONS

The Deltatrac Mk 1 is a very precise metabolic monitor, and is accurate within 3% for gas exchange and EE. RQ is measured with greatest reproducibility and accuracy (within 0.2%), making the monitor particularly suitable for studies of substrate utilisation.

Occurrence of a sequence in marine cyanophages similar to that of T4 g20 and its application to PCR-based detection and quantification techniques

Viruses are ubiquitous components of marine ecosystems and are known to infect unicellular phycoerythrin-containing cyanobacteria belonging to the genus Synechococcus. A conserved region from the cyanophage genome was identified in three genetically distinct cyanomyoviruses, and a sequence analysis revealed that this region exhibited significant similarity to a gene encoding a capsid assembly protein (gp20) from the enteric coliphage T4. The results of a comparison of gene 20 sequences from three cyanomyoviruses and T4 allowed us to design two degenerate PCR primers, CPS1 and CPS2, which specifically amplified a 165-bp region from the majority of cyanomyoviruses tested. A competitive PCR (cPCR) analysis revealed that cyanomyovirus strains could be accurately enumerated, and it was demonstrated that quantification was log-linear over ca. 3 orders of magnitude. Different calibration curves were obtained for each of the three cyanomyovirus strains tested; consequently, cPCR performed with primers CPS1 and CPS2 could lead to substantial inaccuracies in estimates of phage abundance in natural assemblages. Further sequence analysis of cyanomyovirus gene 20 homologs would be necessary in order to design primers which do not exhibit phage-to-phage variability in priming efficiency. It was demonstrated that PCR products of the correct size could be amplified from seawater samples following 100x concentration and even directly without any prior concentration. Hence, the use of degenerate primers in PCR analyses of cyanophage populations should provide valuable data on the diversity of cyanophages in natural assemblages. Further optimization of procedures may ultimately lead to a sensitive assay which can be used to analyze natural cyanophage populations both quantitatively (by cPCR) and qualitatively following phylogenetic analysis of amplified products.

Prediction of body composition in elderly men over 75 years of age

A comprehensive number of body composition predictions (involving weight, height, skinfold thicknesses, bioelectrical impedance and near-infrared interactance-NIRI) were evaluated against total body water (TBW from isotope dilution), in 23 randomly selected men over 75 years old, and dual-energy X-ray absorptiometry (DXA), in 15 volunteers from this group. Comparisons were made between anthropometric and impedance methods for estimating limb muscle mass (obtained using DXA). Bias and 95% limits of agreement between measured TBW and DXA estimates were -2.1 kg and 3.1 kg, respectively (for fat, 5.4% and 6.1% body weight). Agreement between TBW predictions and reference measurements was remarkably variable, irrespective of whether TBW was predicted from TBW-specific equations or indirectly from estimates of fat or fat-free mass: for predictions using anthropometry, bias ranged from -4.7 kg to 1.6 kg and 95% limits of agreement from bias +/- 3.8 kg to +/- 5.0 kg; using impedance, bias was -8.8 kg to 3.2 kg and 95% limits of agreement were bias +/- 3.6 kg to +/- 7.8 kg; corresponding values for NIRI were -5.3 kg and +/- 5.4 kg. Although some non-age-specific equations appeared valid, age-specific equations generally predicted TBW better. Limb muscle mass (DXA) was predicted better using the segmental impedance method, from indices of limb muscle area (r = 0.76; SEE = 1.9 kg) and volume (r = 0.86; SEE = 1.6 kg), than by anthropometry alone (r = 0.61 and 0.71; SEE = 2.3 kg and 2.1 kg, respectively). In conclusion, some body composition predictions are unacceptable (at least for TBW) in older men, and care is recommended when selecting from these methods or equations. Also, the segmental impedance method is as good as, if not better than, anthropometry alone in predicting limb muscle mass (DXA) in older men.

Components of total energy expenditure in free-living elderly men (over 75 years of age): measurement, predictability and relationship to quality-of-life indices

Current recommendations for energy requirements in the elderly are based on assumed levels of physical activity relative to BMR (1.5 x BMR). The main aim of the present study was to establish whether these recommendations might be applicable to a randomly-selected group of free-living elderly men (all over 75 years of age). BMR was measured by indirect calorimetry and total energy expenditure (TEE) by the doubly-labelled-water technique. Further aims included evaluating the applicability of a variety of BMR prediction equations and whether assessed quality of life reflected any measured indices of energy expenditure. The mean value for daily energy requirement was found to be 1.5 x BMR (89 J/kg per min) but with substantial inter-individual variation (sd 0.2 x BMR; 14 J/kg per min). The bias between measured TEE and TEE estimated (1.5 x BMR) from the various BMR predictions varied according to which equation was used (-10- + 8% of the mean) with substantial 95% limits of agreement (28-30% of the mean). TEE and physical activity plus thermogenesis (TEE-BMR) were positively related to activities of daily living, but no relationships were apparent between these and perceived quality of life. It is concluded that, despite considerable inter-individual variability, national recommendations for energy requirements of elderly people are applicable to this randomly-selected group of free-living men over 75 years of age but that substantial variation exists when attempts are made to estimate TEE from measurements or predictions of BMR.

Estimating energy expenditure from specific activity of urine urea during lengthy subcutaneous NaH14CO3 infusion

Five healthy male subjects were continuously infused subcutaneously with [14C]bicarbonate (12.3 microCi/day) using a mini pump for 5 days while in a whole body calorimeter. Energy expenditure was varied over a range of 1.35-1.75 times basal metabolic rate. Urine collections were obtained throughout the study and used to measure the specific activity of urea, from which CO2 production was estimated. It was assumed that the recovery of label in gaseous CO2 was 95% of that infused and that the specific activity of urea was 85% that of expired CO2. Continuous daily collections of calorimeter air revealed that 95.6 +/- 1.3% (SD) of infused label was recovered as gaseous CO2, with little daily variation. Another 1.5 +/- 0.4% was recovered as urinary urea. The estimated CO2 production, calculated from the specific activity of urea in 24-h urine samples corrected for the small effects due to changes in the size and specific activity of the urea pool, was found to be 100 +/- 5% of the calorimeter estimate for 1-day periods (20.80 +/- 1.44 mol CO2/day) and 100 +/- 2% for 4-day periods. This study suggests that, in healthy subjects, the labeled [14C]bicarbonate-urea method can provide reasonable estimates of net CO2 production over the range examined.

Comparative evaluation of body composition methods and predictions, and calculation of density and hydration fraction of fat-free mass, in obese women

The objective of this study was to apply a three-component model of body composition to a group of obese women in order to (a) establish the relative value of a number of readily available prediction equations by comparison of the extent of agreement between these predictions and body composition estimated by the model and other reference methods and (b) evaluate density and hydration of fat-free mass. Estimation of body composition was carried out by reference methods and prediction equations and the usefulness of these prediction equations for application specifically to obese women was evaluated. The subjects were 15 obese, otherwise healthy, Caucasian women (body mass index > 30kg/m2 and body fat > 40% of body weight, as originally determined using densitometry). Body composition was estimated using three established reference methods (deuterium dilution which primarily measures total body water, densitometry for body fat and fat-free mass and total body potassium) and the three component model constructed from deuterium dilution and densitometry. Density and hydration fraction of the fat-free mass were calculated from appropriate values obtained as integral parts of the three-component model. In addition, body composition was predicted from various prediction equations incorporating weight and height (some of which include a factor for age), from a number of prediction equations utilizing different terms involving the same whole-body bio-electrical impedance measurement and from measurements of skinfold thickness and near infrared interactance. The extent of agreement between methods was assessed using bias and 95% limits of agreement. Mean density of fat-free mass was found to be 1.104 kg/l (s.d. 0.006kg/l) with a range of 1.093 to 1.117 kg/l, and mean hydration fraction was 0.712 (s.d. 0.016) with a range of hydration from 68.2% to 75.1% (all values were calculated from the three-component model). In general, the reference methods (densitometry, deuterium dilution, the three-component model and total body potassium) demonstrated better agreement with each other than with the prediction methods or equations. In these obese women, skinfold thickness measurements are apparently less reliable (large bias and 95% limits of agreement) than in the lean subjects of a variety of other studies. A majority of interpretations of weight and height measurements and predictions incorporating impedance/resistance measurements are apparently not applicable to this group of obese women, due to large values for both bias and 95% limits of agreement.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of abilities of various interpretations of bio-electrical impedance to predict reference method body composition assessment

Body composition was assessed in 28 normal men and women using three established reference methods (deuterium dilution for total body water, and densitometry and dual-energy X-ray absorptiometry for body fat and fat-free mass), the four- and three-component models based on these methods, and eight different predictions of the same whole-body bio-electrical impedance measurement. The comparative value of each prediction was assessed using bias and 95% limits of agreement against all reference methods. The magnitude of bias between each interpretation of whole body impedance and each reference method estimate was found to vary considerably, but in general this was consistent over the range studied. However, with few exceptions, magnitudes of the limits of agreement were considerable. For example, a majority of values of 95% limits of agreement in predicting total body water reached bias+/-3 kg or above, and all values in predicting fat (% body weight) for all subjects reached bias+/-6%, and for most purposes these could well be unacceptable. Although in absolute terms bias and limits of agreement for fat-free mass were the same as for body fat, estimates of fat-free mass were relatively more acceptable because fat-free mass was (as is the usual case) the larger of these two body components.

Measurement of bicarbonate turnover in humans: applicability to estimation of energy expenditure

Bicarbonate turnover and energy expenditure were assessed in six healthy male volunteers, by the use of a constant infusion of radiolabeled bicarbonate (NaH14CO3) administered over 36 h, while the volunteers were confined to a whole body indirect calorimeter. Recovery and dilution of isotope were assessed from measurements made on continuous collections of CO2, entering and leaving the calorimeter, urine, and intermittent spot breath and saliva samples. Mean recovery of infused label in gaseous CO2 was 95.6 +/- 1.1% (SD) between 12 and 36 h. Applying a 95% mean recovery of label to each subject individually enabled the use of integrated mean specific activity of CO2 in spot breath and urine samples to predict measured net CO2 production and energy expenditure to within about +/- 6%. Estimates based on urinary measurements were compromised slightly by the exchange of label through the bladder wall (this was dependent on pH and volume of urine). It is concluded that this constant-infusion labeled bicarbonate method offers a potentially useful means of assessing net CO2 production and total energy expenditure over the short term (e.g., 1-3 days).

Four-component model for the assessment of body composition in humans: comparison with alternative methods, and evaluation of the density and hydration of fat-free mass

1. Body composition was assessed in 28 healthy subjects (body mass index 20-28 kg/m2) by dual-energy X-ray absorptiometry, deuterium dilution, densitometry, 40K counting and four prediction methods (skinfold thickness, bioelectrical impedance, near-i.r. interactance and body mass index). Three- and four-component models of body composition were constructed from combinations of the reference methods. The results of all methods were compared. Precision was evaluated by analysis of propagation of errors. The density and hydration fraction of the fat-free mass were determined. 2. From the precision of the basic measurements, the propagation of errors for the estimation of fat (+/- SD) by the four-component model was found to be +/- 0.54 kg, by the three-component model, +/- 0.49 kg, by deuterium dilution, +/- 0.62 kg, and by densitometry, +/- 0.78 kg. Precision for the measurement of the density and hydration fraction of fat-free mass was +/- 0.0020 kg/l and +/- 0.0066, respectively. 3. The agreement between reference methods was generally better than between reference and alternative methods. Dual-energy X-ray absorptiometry predicted three- and four-component model body composition slightly less well than densitometry or deuterium dilution (both of which greatly influence these multi-component models). 4. The hydration fraction of fat-free mass was calculated to be 0.7382 +/- 0.0213 (range 0.6941-0.7837) and the density of fat-free mass was 1.1015 +/- 0.0073 kg/l (range 1.0795-1.1110 kg/l), with no significant difference between men and women for either. 5. The results suggest that the three- and four-component models are not compromised by errors arising from individual techniques.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of the composition of major body regions by dual-energy X-ray absorptiometry (DEXA), with special reference to limb muscle mass

Dual-energy X-ray absorptiometry (DEXA) has been used to assess and compare the composition of whole body and major body regions in 12 female (weight, 56.9 +/- 6.2 kg; BMI, 17-25 kg m-2) and 16 male (weight, 73.1 +/- 9.6 kg; BMI, 20-28 kg m-2) healthy subjects. Standard deviations (and % coefficients of variation) of the differences between repeated measurements of fat ranged from 0.11 kg (9.0%) for arms to 0.42 kg (3.0%) for whole body; for arm bone mineral, 0.01 kg (2.0%), and for fat-free soft tissue of the whole body, 0.42 kg (0.8%). Limb muscle mass was estimated using a new theoretical model of body composition, and the corresponding precision ranged from 0.15 kg (3.8%) to 0.27 kg (1.5%) for arms and total limb muscle mass, respectively. Proportions of each region consisting of fat were greater in females than in males (range, 20-31% vs. 16-18%), respectively, but the ratio of trunk to leg fat was lower (34:49% vs. 46:38%, respectively). Regional proportions of bone were similar between the sexes (all in the range 2.9-5.6%, for both females and males). Mean total limb muscle masses were 14.2 kg (arms, 2.8 kg; legs, 11.4 kg) for females and 22.2 kg (arms, 4.8 kg; legs, 17.4 kg) for males, which were 33.6% and 36.0% of fat-free mass, respectively. The correlation coefficients between limb muscle (DEXA) and other indices of muscle mass were: for DEXA vs. total body potassium, 0.90 (SEE 1.1 kg muscle mass) to 0.94 (1.6 kg); and for DEXA vs. anthropometry, 0.43 (1.2 kg) to 0.85 (1.3 kg). Those for limb volume (DEXA) vs. anthropometric volume, 0.91 (0.78 1) to 0.94 (1.91 1). It is concluded that DEXA enables the valid and reproducible estimation of fat, fat-free soft tissue, bone, and limb muscle mass.

Plasma folate levels in preterm infants, with and without a 1 mg daily folate supplement

One hundred and four preterm infants were studied during the first few months of life in the Special Care Baby Unit of Addenbrooke's Hospital, Cambridge, United Kingdom. Previously, it had been the daily practice within the Unit to give a 1 mg oral supplement of folate (in the form of pteroylglutamic acid), once the infants had commenced full enteral feeding. At least one blood sample was obtained from 70 infants before oral folate supplementation was started. In these, the plasma folate levels fell progressively from a median value of 45 micrograms/l to a median of 12 micrograms/l, by the 2nd-3rd week of life. Once started on the oral supplement, 83 of the infants provided at least one blood sample. The plasma folate level of these infants rose immediately to a median value of 300 micrograms/l and a maximum of 1000 micrograms/l. Within individuals, these plasma folate levels decreased progressively following the introduction of the supplement, despite continuing daily supplementation. In a typical baby this decrease appeared to be explained by an increase in body-size, i.e. dilution of the folate into a larger pool. The implications of this level of supplementation are discussed, and in the light of our observations we suggest that daily supplementation in the range, 0.05-0.2 mg folate may be preferable for well preterm infants.

High folate intakes related to zinc status in preterm infants

The former practice of giving 1 mg (2.27 mumoles) oral folic acid daily to premature infants receiving enteral feeds was assessed with respect to zinc status in Cambridge, United Kingdom. A group of 60 preterm infants, 80% of whom were receiving 1 mg oral folic acid daily, were studied for up to the first 16 weeks of life. Plasma folate and plasma zinc were measured for each subject. A significant inverse relationship was found between the maximum attained serum folate level and the minimum attained serum zinc level, (t = 5.0, 58 df, P less than 0.0001). This remained significant after corrections had been made for gestational age at birth, fetal growth retardation, birth weight, sex, diet, assisted ventilation and length of time to full enteral feeding. The hypothesis that very high folate intakes may adversely affect serum zinc levels and, by inference, zinc status in preterm infants could not be rejected. Caution is therefore advised when prescribing such very high folate doses daily for small preterm infants.

Inter-observer variability in the measurement of body composition

The inter-observer variation in simple bedside assessments of body composition has been evaluated in 12 healthy adult subjects (6 male and 6 female) by 6 observers. Systematic bias between observers was found to be evident in each of the basic measurements (except height) and in each of the estimates of body composition (except those derived from weight and height alone). The largest residual coefficients of variation (rCV) for the basic measurements were found for skinfold thickness (11-18 per cent for individual skinfold thicknesses, and 9 per cent for the sum of four skinfold thicknesses), and the lowest for weight (0.01 per cent for digital scales, and 0.05 per cent for beam balance) and height (0.4 per cent). The rCV for whole-body resistance (1.2 per cent), forearm resistance (5.4 per cent) and near infra-red interactance (optical density 1: 5.6 per cent and optical density 2: 6.2 per cent) measurements were found to have intermediate values. The variability in the estimate of body fat obtained by skinfold thickness (rCV = 4.6 per cent) and near infra-red interactance methods (rCV = 4.2 per cent) was found to be greater than that from the resistance method (rCV = 2.6 per cent) and by methods based on weight and height alone (rCV = 1.1 per cent). The variability in the estimate of fat-free mass showed the same trend as that for body fat, but the rCVs were less due to the greater mass of the fat-free body compared to body fat.(ABSTRACT TRUNCATED AT 250 WORDS)

Potential use of bioelectrical impedance of the 'whole body' and of body segments for the assessment of body composition: comparison with densitometry and anthropometry

The value of 'whole body' and segmental impedance measurements, and of simple anthropometric methods for predicting body composition was assessed in 24 normal (14m, 10f) subjects (BMI, 18.3-28.6), using densitometry as the reference method. The contribution of segmental impedance was assessed in a separate group of 24 normal (12m, 12f) subjects (BMI, 19.8-28.8) at two frequencies (1 kHz and 50 kHz). Estimates of specific resistivities of certain individual segments (upper arm, forearm, upper leg, and lower leg) were also made in this group, and compared to those obtained from a group of 7 obese female subjects (BMI, 32.6-56.1). The bias and 95 per cent limits of agreement between densitometrically determined body composition (fat and fat-free mass, and total body water) and the alternative methods were found to vary considerably, depending on the technique and/or equations employed. Estimates of whole body composition based on impedance or resistance measurements were found to be associated with only slightly smaller limits of agreement than those made by anthropometry. The upper limb was found to have the greatest influence on whole body impedance measurements. Indeed, the forearm, which accounts for 1.3 per cent of body weight contributes 25.0 per cent to 'whole body' impedance. The estimated specific resistivities of segments were found to be considerably greater in the obese individuals than in normal female subjects (for example, 75 per cent higher for the upper arm, P less than 0.001). The results suggest that: (a) there may be a systematic, population-related, error in predicting densitometric estimates of body composition with the use of standard equations, which incorporate variables such as weight, height, skinfold thicknesses, and impedance/resistance measurements; (b) in this population, impedance or resistance measurements confer only a small advantage over simple anthropometry for predicting body composition; (c) the impedance of the arm or leg may provide a simple alternative method for assessing the composition of the whole body; and (d) the estimated specific resistivity of individual body segments may be useful for assessing the composition of those segments.

Does mitochondrial compartmentation of CO2 exist in man?

A comparison was made between the specific radioactivity of urea, and that of CO2 in breath, in urine and in arterialized blood, during a 36-h continuous infusion of 0.5 mCi and 100 mmol of sodium bicarbonate (NaH14CO3) into six normal male volunteers. After a period of equilibration, the mean specific radioactivity of urea was found to be only 16% below that of end expiratory CO2 and a similar amount below that of CO2 both in arterialized blood and in urine. This difference may be explained by isotopic dilution of 14CO2 by metabolic CO2 produced in the splanchnic tissues. It is concluded that, in these normal subjects, there is little or no compartmentation between cytosolic CO2 and the mitochondrial CO2 used for urea synthesis.

Factors influencing the production of creatinine: implications for the determination and interpretation of urinary creatinine and creatine in man

The rates of creatine/creatinine inter-conversions and their equilibrium were studied under controlled conditions of temperature and pH that simulate urine storage conditions. The concentrations and ratios of creatine to creatinine in urine obtained from subjects with various pathophysiological conditions were determined, both before and after storage. The observed changes occurring during storage were compared with predicted changes based on observations of standard solutions. The initial reaction rate was found to increase with temperature, occurring maximally at about pH 3.7 for the conversion of creatine to creatinine, and at about pH 5.0 for the conversion of creatinine to creatine. At low pHs the equilibrium position was displaced towards creatinine. Above about pH 6.0 the equilibrium was associated with approximately equimolar quantities of creatine and creatinine. The creatine content of urine ranged from virtually nil to about double that of creatinine and changed predictably during storage. These findings have implications for the use of creatinine as an index of muscle mass and nutritional status, and as a marker for the completeness of urine collections.