Tracking the Oxidative and Nonoxidative Fates of Isotopically Labeled Nutrients in Animals

McCue, Marshall D.

doi:10.1525/bio.2011.61.3.7

Cited by 40 publications

(30 citation statements)

References 67 publications

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“…To evaluate the preferential routing of labeled leucine to each tissue in blackcaps, we compared the isotope ratios of each tissue with the isotope ratio of total body N, assuming the tracer was homogeneously distributed in the body after administration (McCue, 2011;McCue et al, 2011a). Making the assumption of homogeneous distribution is prudent and conservative because there are no published estimates of N turnover rates for organs of blackcaps or other small songbirds.…”

Section: Stable Isotopesmentioning

confidence: 99%

Allocation of endogenous and dietary protein in the reconstitution of the gastrointestinal tract in migratory blackcaps at stopover sites

Muñoz‐Garcia

Aamidor

McCue

et al. 2012

Journal of Experimental Biology

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SUMMARYDuring migratory flight, the mass of the gastrointestinal tract (GIT) and its associated organs in small birds decreases in size by as much as 40%, compared with the preflight condition because of the catabolism of protein. At stopover sites, birds need 2-3days to rebuild their GIT so that they can restore body mass and fat reserves to continue migration. The source of protein used to rebuild the GIT may be exogenous (from food ingested) or endogenous (reallocated from other organs) or both. Because the relative contribution of these sources to rebuild the GIT of migratory birds is not yet known, we mimicked in-flight fasting and then re-feeding in two groups of blackcaps (Sylvia atricapilla), a Palearctic migratory passerine. The birds were fed a diet containing either 3% or 20% protein to simulate different refueling scenarios. During re-feeding, birds received known doses of 15 N-L-leucine before we measured the isotope concentrations in GIT and associated digestive organs and in locomotory muscles. We then quantified the extent to which blackcaps rebuilt their GIT with endogenous and/or dietary protein while refeeding after a fast. Our results indicate that blackcaps fed the low-protein diet incorporated less exogenous nitrogen into their tissues than birds fed the 20% protein diet. They also allocated relatively more exogenous protein to the GIT than to pectoral muscle than those birds re-fed with the high-protein diet. However, this compensation was not sufficient for birds eating the low-protein diet to rebuild their intestine at the same rate as the birds re-fed the high-protein diet. We concluded that blackcaps must choose stopover sites at which they can maximize protein intake to minimize the time it takes to rebuild their GIT and, thus, resume migration as soon as possible.

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Section: Stable Isotopesmentioning

confidence: 99%

Allocation of endogenous and dietary protein in the reconstitution of the gastrointestinal tract in migratory blackcaps at stopover sites

Muñoz‐Garcia

Aamidor

McCue

et al. 2012

Journal of Experimental Biology

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“…Even if 2 H atoms can be exchanged with other organic pools beyond the biochemical routes of lipid metabolism, providing the birds with deuterated drinking water between the intraperitoneal injection and tissue sampling assured a consistent labelling capacity as confirmed by the final body water 2 H-enrichment. Despite the incomparable specificity obtained by direct traceability of a particular substrate (as reviewed by McCue, 2011), its delivery and dosage may also influence the response of these metabolic pathways by being absorbed and/or oxidized differently. Another option would be resolving the 2 H-enrichment levels of specific FA compared with the presented aggregated analysis of enrichment by 2 H NMR.…”

Section: Discussionmentioning

confidence: 99%

Metabolic plasticity for subcutaneous fat accumulation in a long distance migratory bird traced by 2H2O

Viegas

Araújo

Rocha

et al. 2017

Journal of Experimental Biology

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The migrant black-tailed godwit (Limosa limosa) traditionally used natural wetlands in the Iberian Peninsula to prepare for migratory flights by feeding mainly in estuaries. In recent decades, this species has become increasingly dependent on rice fields, thereby relying on a plant-based diet for fuelling. Dietary fatty acids (FA) seem to be determinant to the composition of accumulated subcutaneous fat in migratory birds. It is still unclear whether metabolic plasticity allows for modification and/or synthesis of FA, contributing to a lipid profile that enables a successful migratory performance. Deuterated water was administered to captive black-tailed godwits submitted to two diets (fly larvae versus rice) and the incorporation of deuterium ( 2 H) into subcutaneous triglycerides was analyzed by NMR. A recently developed localized biopsy method for sampling subcutaneous fat was employed with later successful release of all birds into the wild. The average chemical structure reflected mostly a mixture of saturated and monounsaturated 16-and 18-carbon FA, a profile frequently found in migrant birds. Significantly higher levels of polyunsaturated FA, as well as detectable levels of n-3 FA, were observed in fly-larvae-fed birds. Excess 2 H-enrichments in FA revealed significantly higher rates of fractional de novo lipogenesis and FA desaturation capacity in rice-fed birds. This novel and nonlethal tracer method revealed the capacity of this species to alter its lipid metabolism to compensate for a poorer dietary lipid contribution. Because of its versatility, adapting this method to other scenarios and/or other migratory species is considered feasible and costeffective.

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“…An increasing number of studies in comparative physiology have also begun using 13 CO 2 -breath testing to explore the nutrient oxidation and bioenergetics in animals (Carleton et al, 2006;Hughes et al, 2008;McCue et al, 2010McCue et al, , 2011aSponheimer et al, 2006;Voigt et al, 2008aVoigt et al, , 2010Welch et al, 2008;Welch & Suarez, 2007). 13 C is a stable isotope thus 13 CO 2 -breath testing offers a safe alternative to the use of radioactive, 14 C-labeled tracers, an important factor for pediatric or pregnant patients (Bodamer & Halliday, 2001;Braden et al, 2007;Christian et al, 2002;Evenpoel et al, 2000;Rating & Langhans, 1997) and studies involving wild animals (Ayliffe et al, 2004;Hatch et al, 2002;McCue, 2011;Sponheimer et al, 2006;Voigt et al, 2003Voigt et al, , 2008a.…”

Section: Isotopes and Breath Testingmentioning

confidence: 99%

“…However, most research exploring the oxidative fates of exogenous proteins in vivo does not employ isotopically labeled proteins, but rather purified 13 C-labeled amino acid tracers under the assumption that these free amino acids 'behave' exactly like those amino acids that are biochemically integrated into proteins (Braden, 2009;Fischer & Wetzel, 2002;Ghoos & Beaufrere, 1998;McCue, 2011). Recent studies have shown that this assumption may not be appropriate (Boirie et al, 1996;Conceicao et al, 2007;Daenzer et al, 2001;Dangin et al, 2001;Deglaire et al, 2009;Hughes et al, 2008;Koopman et al, 2009;Metges et al, 2000;Ronnestad et al, 2000;Zarate et al, 1999).…”

Section: Amino Acid Tracers Are Not the Same As Protein Tracersmentioning

confidence: 99%

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Hens Produce Artificially Enriched 13C Egg Proteins for Metabolic Tracer Studies

McCue

Arquisola²,

Albach³

et al. 2013

IJB

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Clinicians and researchers studying protein metabolism in vivo, typically use isotopically-labeled free amino acids as metabolic tracers rather than isotopically-labeled proteins because such proteins are commercially unavailable. However, the use of free amino acids in lieu of protein tracers violates the critical assumption that tracer molecules undergo the identical biochemical reactions as the tracee molecules of interest. To address this problem we synthesized 13 C-labeled proteins using egg laying hens and investigated the relationship between tracer dose and method of delivery on 13 C-protein production. We enriched hens with one of two isotope tracers ( 13 C-1-leucine or a uniformly labeled 13 C-amino acid mixture) mixed in their food or dissolved in their drinking water at different dosing levels (86-432 mg day -1 ). The recovery of 13 C in egg white proteins of the hen fed 13 C-leucine ranged from 14% to 21%; recovery rates were highest at the lowest dosing level. At the highest dosing level egg whites were enriched more than 150‰ above background levels of 13 C. The time required for half maximal 13 C enrichment depended chiefly on the mode of tracer administration, and ranged from 2.5 days for 13 C-leucine dissolved in water to 4.9 days for 13 C-leucine mixed in food. Relative rates of 13 C recovery in the egg protein were lowest for hens fed the uniformly 13 C labeled amino acid mixture, presumably because of the high proportion of nonessential amino acids. The time required for the 13 C-enrichment in eggs to return to background levels at the end of the enrichment period was about twice that required to initially reach isotopic equilibrium with the diet, indicating significant biochemical discrimination of endogenous 13 C amino acids. We conclude that delivering small amounts of 13 C amino acid tracers in the drinking water of hens is the most effective way to produce 13 C-enriched proteins to for tracer studies that do not require δ 13 C-enrichment above 200‰.

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Tracking the Oxidative and Nonoxidative Fates of Isotopically Labeled Nutrients in Animals

Cited by 40 publications

References 67 publications

Allocation of endogenous and dietary protein in the reconstitution of the gastrointestinal tract in migratory blackcaps at stopover sites

Allocation of endogenous and dietary protein in the reconstitution of the gastrointestinal tract in migratory blackcaps at stopover sites

Metabolic plasticity for subcutaneous fat accumulation in a long distance migratory bird traced by 2H2O

Hens Produce Artificially Enriched 13C Egg Proteins for Metabolic Tracer Studies

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