Nitrogen (N) isotopic discrimination (i.e. the difference in natural .sup.15 N abundance between the animal proteins and the diet; DELTA.sup.15 N) is known to correlate with N use efficiency (NUE) ...and feed conversion efficiency (FCE) in ruminants. However, results from the literature are not always consistent across studies, likely due to isotopic discrimination pathways that may differ with the nature of diets. The objective of the present study was to assess at which level, from rumen to tissues, DELTA.sup.15 N originates and becomes related to NUE and FCE in fattening yearling bulls when they are fed two contrasted diets. Twenty-four Charolais yearling bulls were randomly divided into two groups and fed during 8 months, from weaning to slaughter, either 1) a high starch diet based on corn silage supplying a balanced N to energy ratio at the rumen level (starch) or 2) a high fiber diet based on grass silage supplying an excess of rumen degradable N (fiber). All animals were slaughtered and samples of different digestive pools (ruminal, duodenal, ileal and fecal contents), animal tissues (duodenum, liver and muscle), blood and urine were collected for each animal. Ruminal content was further used to isolate liquid-associated bacteria (LAB), protozoa and free ammonia, while plasma proteins were obtained from blood. All samples along with feed were analyzed for their N isotopic composition. For both diets, the digestive contribution (i.e. the N isotopic discrimination occurring before absorption) to the DELTA.sup.15 N observed in animal tissues accounted for 65 #177; 11%, leaving only one third to the contribution of post-absorptive metabolism. Concerning the DELTA.sup.15 N in digestive pools, the majority of these changes occurred in the rumen (av. DELTA.sup.15 N = 2.12 #177; 0.66%), with only minor .sup.15 N enrichments thereafter (av. DELTA.sup.15 N = 2.24 #177; 0.41%), highlighting the key role of the rumen on N isotopic discrimination. A strong, significant overall relationship (n = 24) between DELTA.sup.15 N and FCE or NUE was found when using any post-absorptive metabolic pool (duodenum, liver, or muscle tissues, or plasma proteins; 0.52 r 0.73; P less than or equal to 0.01), probably as these pools reflect both digestive and post-absorptive metabolic phenomena. Fiber diet compared to starch diet had a lower feed efficiency and promoted higher (P less than or equal to 0.05) DELTA.sup.15 N values across all post-absorptive metabolic pools and some digestive pools (ruminal, duodenal, and ileal contents). The within-diet relationship (n = 12) between DELTA.sup.15 N and feed efficiency was not as strong and consistent as the overall relationship, with contrasted responses between the two diets for specific pools (diet x pool interaction; P less than or equal to 0.01). Our results highlight the contrasted use of N at the rumen level between the two experimental diets and suggests the need for different equations to predict FCE or NUE from DELTA.sup.15 N according to the type of diet. In conclusion, rumen digestion and associated microbial activity can play an important role on N isotopic discrimination so rumen effect related to diet may interfere with the relationship between DELTA.sup.15 N and feed efficiency in fattening yearling bulls.
Exclusively breastfed infants born to obese mothers have previously been shown to gain less weight by 1-month postpartum than infants of normal-weight mothers. Our hypothesis is that human milk ...composition and volume may differ between obese and normal-weight mothers.
To compare human milk leptin, macronutrient concentration, and volume in obese and normal-weight mothers. Mother and infant characteristics were studied as secondary aims.
This cross-sectional observational study compared 50 obese mothers matched for age, parity, ethnic origin, and educational level with 50 normal-weight mothers. Leptin, macronutrient human milk concentration, and milk volume were determined at 1 month in exclusively breastfed infants. Mother characteristics and infant growth were recorded.
Human milk leptin concentration was higher in obese mothers than normal-weight mothers (4.8±2.7 vs. 2.5±1.5 ng.mL-1, p<0.001). No difference was observed between obese and normal-weight mothers in protein, lipid, carbohydrate content, and volume, nor in infant weight gain.
Leptin concentration was higher in the milk of obese mothers than that of normal-weight mothers, but macronutrient concentration was not. It remains to be established whether the higher leptin content impacts on infant growth beyond the 1-month of the study period.
Abstract
We pay tribute to Marshall Joffe, PhD, and his substantial contributions to the field of causal inference with focus in biostatistics and epidemiology. By compiling narratives written by us, ...his colleagues, we not only present highlights of Marshall’s research and their significance for causal inference but also offer a portrayal of Marshall’s personal accomplishments and character. Our discussion of Marshall’s research notably includes (but is not limited to) handling of posttreatment variables such as noncompliance, employing G-estimation for treatment effects on failure-time outcomes, estimating effects of time-varying exposures subject to time-dependent confounding, and developing a causal framework for case-control studies. We also provide a description of some of Marshall’s unpublished work, which is accompanied by a bonus anecdote. We discuss future research directions related to Marshall’s research. While Marshall’s impact in causal inference and the world outside of it cannot be wholly captured by our words, we hope nonetheless to present some of what he has done for our field and what he has meant to us and to his loved ones.
Stable isotopes have been widely used to monitor remediation of environmental contaminants over the last decades. This approach gives a good mechanistic description of natural or assisted degradation ...of organic pollutants, such as methyl tert-butyl ether (MTBE). Since abiotic degradation seems to be the most promising assisted attenuation method, the isotopic fractionation associated with oxidation and hydrolysis processes need to be further investigated in order to understand better these processes and make their monitoring more efficient. In this study, position-specific isotope effects (PSIEs) associated with permanganate oxidation and acid hydrolysis of MTBE were determined using isotope ratio monitoring by 13C Nuclear Magnetic Resonance Spectrometry (irm-13C NMR) combined with isotope ratio monitoring by Mass Spectrometry (irm-MS). The use of this Position-Specific Isotopic Analysis (PSIA) method makes it possible to observe a specific normal isotope effect (IE) associated with each of these two abiotic degradation mechanisms. The present work demonstrates that the 13C isotope pattern of the main degradation product, tert-butyl alcohol (TBA), depends on the chemical reaction by which it is produced. Furthermore, this study also demonstrates that PSIA at natural abundance can give new insights into reaction mechanisms and that this methodology is very promising for the future of modeling the remediation of organic contaminants.
•Determination of Position-Specific Isotope Effects (PSIEs).•PSIEs associated with permanganate oxidation and acid hydrolysis of MTBE.•Use of PSIEs for chemical mechanisms elucidation.•Modeling of PSIEs associated with MTBE remediation.
Root exudation is considered to regulate the abundance of the microbial community. It may vary both qualitatively and quantitatively in response to the environment in which the plant is growing. A ...part of exuded N derives from amino acids (AAs). This, in turn, may help plants to cope with abiotic stresses by favouring positive interactions with the rhizosphere environment, thus playing a potential role in maintaining healthy plants. In this respect, an under-investigated area is the effect of stress due to water deficit (WD). It is proposed that the AA profile in the rhizosphere may be altered by WD, reflecting a modulation of root AA exudation linked to a physiological response of the plant to water stress. To investigate this, Pisum sativum L. plants, grown in unsterilised Rhizobium leguminosarum-enriched soil, were stem-labelled with 15N-urea for 96 h, and then subjected/not subjected to 72 h of WD. The concentrations and abundance of 15N-labelling in individual AAs were determined in both roots and the associated rhizosphere at 24, 48 and 72 h after stress application. It was found that both AAs metabolism in the pea root and AAs exudation were strongly modified in WD conditions. After 24 h of WD, the concentrations of all measured AAs increased in the roots, accompanied by a dramatic stress-related increase in the 15N-labelling of some AAs. Furthermore, after 48–72 h of WD, the concentrations of Pro, Ala and Glu increased significantly within the rhizosphere, notably with a concomitant increase in 15N-enrichment in Pro, Ser, Asn, Asp, Thr and Ile. These results support the concept that, in response to WD, substantial amounts of recently assimilated N are rapidly translocated from the shoots to the roots, a portion of which is exuded as AAs. This leads to the rhizosphere being relatively augmented by specific AAs (notably HSer, Pro and Ala) in WD conditions, with a potential impact on soil water retention.
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•15N labelled pea plants grown in unsterilised soil were subjected or not to 72 h of water deficit.•After 24 h of stress, AA concentrations in the roots and 15N-labelling of some AAs increased.•After 48 h, the concentrations of Pro and Glu increased significantly within the rhizosphere.•A concomitant and notable increase in 15N-enrichment in Hser, Glu, Ala, Pro and Asn was observed.•Under water stress, recently assimilated N is translocated to the roots and AAs are increasingly released into the soil.
Abstract
Improving the ability of animals to convert feed resources into food for humans is needed for more sustainable livestock systems. Genetic selection for animals eating less while maintaining ...their performance (i.e., low residual feed intake RFI) appears a smart strategy but its effectiveness relies on high-throughput animal phenotyping. Here, we explored plasma nitrogen (N) isotope ratios in an attempt to identify easily superior young bulls in terms of RFI. For this, 48 Charolais young bulls fed two contrasting diets (corn vs. grass silage diets) were selected from a larger population as extreme RFI animals (24 low-RFI vs. 24 high-RFI) and their plasma analyzed for natural 15N abundance (δ15N) in the whole protein (bulk protein) and in the individual protein-bound amino acids (PbAA). For the first time, we showed that the δ 15N in plasma bulk protein differed (P = 0.007) between efficient (low-RFI) and inefficient (high-RFI) cattle regardless of diet. Furthermore, most analyzed PbAA followed the same trend as the bulk protein, with lower (P < 0.05) δ 15N values in more efficient (low-RFI) compared with less efficient (high-RFI) cattle, again regardless of diet. The only three exceptions were Phe, Met, and Lys (P > 0.05) for which the first metabolic reaction before being catabolized does not involve transamination, a pathway known naturally to enrich AAs in 15N. The contrasted isotopic signatures across RFI groups only in those PbAA undergoing transamination are interpreted as differences in transamination rates and N-use efficiency between low- and high-RFI phenotypes. Natural isotopic N signatures in bulk proteins and specific PbAA can be proposed as biomarkers of RFI in growing beef cattle fed different diets. However, the current study cannot delineate whether this effect only occurs post-absorption or to some extent also in the rumen. Our data support the conclusion that most efficient cattle in terms of RFI upregulate N conservation mechanisms compared with less efficient cattle and justify future research on this topic.
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•Natural abundance isotope ratio measurement by tandem MS.•Site-specific δ 13 C.•Requires only small sample amounts (nanomols).•Suitable for rapid origin assignment.
Biomolecules ...generally exist as mixtures of diverse isotopologues that differ in the number and sites of rare-isotope substitutions. The exact proportion of isotopologues of a biomolecule may depend on the molecular, cellular, organismal and environmental factors involved in its biosynthesis, localization and consumption. Molecular isotopic structure can thus be a valuable tool to elucidate biochemical mechanisms and for the reconstruction of physiological, ecological and climatic processes. However, little information about this record is accessible by conventional methods of stable isotope chemistry. Here, we report an easy to implement mass spectrometric method that quantifies intramolecular isotope distributions and is specifically designed for use on samples containing low, natural abundances of the rare isotopes. Its essential feature is the use of a narrow initial mass selection window to isolate ions that are heavier due to the presence of one or more isotopic substitutions. This pre-selection greatly increases the relative proportions of the various rare-isotope substituted isotopologues. The selected ions are then fragmented, and within seconds to minutes the isotopic pattern of the fragment peaks reveals information about the intramolecular distribution of isotopes. This approach requires ∼0.1–10 nanomole of analyte, which is about five orders of magnitude less than NMR. We demonstrate the ability to measure the site-specific isotope ratios of metabolites by resolving the 13C content in the amino acid methionine among multiple non-equivalent carbon sites. This technique enables rapid origin assignments for a wide range of organic molecules and can be used for new applications of molecular isotopic structure in medicine and environmental sciences.
Abstract
The genomes of gut Bacteroidales contain numerous invertible regions, many of which contain promoters that dictate phase-variable synthesis of surface molecules such as polysaccharides, ...fimbriae, and outer surface proteins. Here, we characterize a different type of phase-variable system of Bacteroides fragilis, a Type I restriction modification system (R-M). We show that reversible DNA inversions within this R-M locus leads to the generation of eight specificity proteins with distinct recognition sites. In vitro grown bacteria have a different proportion of specificity gene combinations at the expression locus than bacteria isolated from the mammalian gut. By creating mutants, each able to produce only one specificity protein from this region, we identified the R-M recognition sites of four of these S-proteins using SMRT sequencing. Transcriptome analysis revealed that the locked specificity mutants, whether grown in vitro or isolated from the mammalian gut, have distinct transcriptional profiles, likely creating different phenotypes, one of which was confirmed. Genomic analyses of diverse strains of Bacteroidetes from both host-associated and environmental sources reveal the ubiquity of phase-variable R-M systems in this phylum.
Minimal clinically important differences (MCIDs) are used to understand clinical relevance. However, repeated observations produce biased analyses unless one accounts for baseline observation, known ...as regression to the mean (RTM). Using an International Knee Documentation Committee (IKDC) survey dataset, we can demonstrate the effect of RTM on MCID values by (1) MCID-estimate dependence on baseline observation and (2) MCID-estimate bias being higher when the posttest-pretest data correlation is lower. We created 10 IKDC datasets with 5000 patients and a specific correlation under both equal and unequal variances. For each 10-point increase in baseline IKDC, MCID decreased by 3.5, 2.7, 1.9, 1.2, and 0.7 points when posttest-pretest correlations were 0.10, 0.25, 0.50, 0.75, and 0.90, respectively, under equal variances. Not accounting for RTM resulted in a static 20-point MCID. Minimal clinically important difference estimates may be unreliable. Minimal clinically important difference calculations should include the correlation and variances between posttest and pretest data, and researchers should consider using a baseline covariate-adjusted receiver operating characteristic curve analysis to calculate MCID.
Purpose The primary purpose of this study was to determine the effect of the preoperative position of the musculotendinous junction (MTJ) on rotator cuff healing after double-row arthroscopic rotator ...cuff repair. A secondary purpose was to evaluate how tendon length and MTJ position change when the rotator cuff heals. Methods Preoperative and postoperative magnetic resonance imaging (MRI) scans of 42 patients undergoing arthroscopic double-row rotator cuff repair were reviewed. Patients undergoing repairs with other constructs or receiving augmented repairs (platelet-rich fibrin matrix) who had postoperative MRI scans were excluded. Preoperative MRI scans were evaluated for anteroposterior tear size, tendon retraction, tendon length, muscle quality, and MTJ position with respect to the glenoid in the coronal plane. The position of the MTJ was referenced off the glenoid face as either lateral or medial. Postoperative MRI scans were evaluated for healing, tendon length, and MTJ position. Results Of 42 tears, 36 (86%) healed, with 27 of 31 small to medium tears (87%) and 9 of 11 large to massive tears (82%) healing. Healing occurred in 94% of tears that had a preoperative MTJ lateral to the face of the glenoid but only 56% of tears that had a preoperative MTJ medial to the glenoid face ( P = .0135). The measured tendon length increased an average of 14.4 mm in patients whose tears healed compared with shortening by 6.4 mm in patients with tears that did not heal ( P < .001). The MTJ lateralized an average of 6.1 mm in patients whose tears healed compared with medializing 1.9 mm in patients whose tears did not heal ( P = .026). The overall follow-up period of the study was from April 2005 to September 2014 (113 months). Conclusions The preoperative MTJ position is predictive of postoperative healing after double-row rotator cuff repair. The position of the MTJ with respect to the glenoid face is a reliable, identifiable marker on MRI scans that can be predictive of healing. Level of Evidence Level IV, retrospective review of case series; therapeutic study.
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