The measurement of muscle protein synthesis in broilers with a flooding dose technique: use of 15N-labelled phenylalanine, GC-MS and GC-C-IRMS

Effect of an immune challenge and two feed supplements on broiler chicken individual breast muscle protein synthesis rate

Optimization of broiler chicken breast muscle protein accretion is key for the efficient production of poultry meat, whose demand is steadily increasing. In a context where antimicrobial growth promoters use is being restricted, it is important to find alternatives as well as to characterize the effect of immunological stress on broiler chicken's growth. Despite its importance, research on broiler chicken muscle protein dynamics has mostly been limited to the study of mixed protein turnover. The present study aims to characterize the effect of a bacterial challenge and the feed supplementation of citrus and cucumber extracts on broiler chicken individual breast muscle proteins fractional synthesis rates (FSR) using a recently developed dynamic proteomics pipeline. Twenty-one day-old broiler chickens were administered a single 2H2O dose before being culled at different timepoints. A total of 60 breast muscle protein extracts from five experimental groups (Unchallenged, Challenged, Control Diet, Diet 1 and Diet 2) were analysed using a DDA proteomics approach. Proteomics data was filtered in order to reliably calculate multiple proteins FSR making use of a newly developed bioinformatics pipeline. Broiler breast muscle proteins FSR uniformly decreased following a bacterial challenge, this change was judged significant for 15 individual proteins, the two major functional clusters identified as well as for mixed breast muscle protein. Citrus or cucumber extract feed supplementation did not show any effect on the breast muscle protein FSR of immunologically challenged broilers. The present study has identified potential predictive markers of breast muscle growth and provided new information on broiler chicken breast muscle protein synthesis which could be essential for improving the efficiency of broiler chicken meat production. SIGNIFICANCE: The present study constitutes the first dynamic proteomics study conducted in a farm animal species which has characterized FSR in a large number of proteins, establishing a precedent for biomarker discovery and assessment of health and growth status. Moreover, it has been evidenced that the decrease in broiler chicken breast muscle protein following an immune challenge is a coordinated event which seems to be the main cause of the decreased growth observed in these animals.

A novel dynamic proteomics approach for the measurement of broiler chicken protein fractional synthesis rate

RATIONALE

The study of protein synthesis in farm animals is uncommon despite its potential to increase knowledge about metabolism and discover new biomarkers of health and growth status. The present study describes a novel dynamic proteomics approach for the measurement of protein fractional synthesis rate (FSR) in broiler chickens.

METHODS

Chickens received a 10 g/kg oral dose of ² H₂ O at day 21 of their life. Body water ² H abundance was measured in plasma samples using a portable Fourier transform infrared spectrometer. Free and protein-bound amino acids (AAs) were isolated and had their ² H enrichment measured by gas chromatography with mass spectrometry (GC/MS). Peptide ² H enrichment was measured by proteomics analysis of plasma and muscle samples. Albumin, fibrinogen and muscle protein FSR were calculated from GC/MS and proteomics data.

RESULTS

Ala appeared to be more enriched at the site of protein synthesis than in the AA free pools. Glu was found to be the AA closest to isotopic equilibrium between the different AA pools. Glu was used as an anchor to calculate n(AA) values necessary for chicken protein FSR calculation in dynamic proteomics studies. FSR values calculated using proteomics data and GC/MS data showed good agreement as evidenced by a Bland-Altman residual plot.

CONCLUSIONS

A new dynamic proteomics approach for the measurement of broiler chicken individual protein FSR based on the administration of a single ² H₂ O oral bolus has been developed and validated. The proposed approach could facilitate new immunological and nutritional studies on free-living animals.

Effects of dietary energy levels on Pectoralis major mixed muscle protein turnover and body composition in two broiler lines housed in different grow-out environments

This study determined the Pectoralis (P) major mixed muscle protein turnover (PT) in two meat broiler lines, Line A and Line B, during the finishing grow-out feeding period (21-42 days) as affected by the dietary metabolizable energy (ME) levels and ambient temperatures. Experimental finishing diets consisted of 80, 90, 100, 110 and 120% ME of recommended nutrient guidelines for energy level. Fractional synthesis rates (FSR) or fractional degradation rates (FDR) were measured in P. major at day 36 and 42. Protein and fat mass gain were measured, and respective energy retention efficiencies as protein and fat (EREp and EREf) were determined. Metabolic heat production (HP) was also reported. Experimental feeding studies were conducted in cool season (24 hr mean: 69.91˚F and 63.98% RH) and in hot season (24 hr mean: 77.55˚F and 86.04% RH). Results showed that FSR or FDR values were not affected by dietary ME levels at day 36, whereas reduced FSR (p < .05) were observed at day 42 fed diets with reduced ME levels (≤100% ME) which could have resulted from greater maintenance energy requirement of maturing broilers at that age. Broilers fed reduced ME diets (≤100% ME) maintained protein mass (equivalent to broilers fed ≥100%-120% ME) by reduced FDR and increased feed intake. Grow-out ambient temperature did not affect FSR or FDR values across ME levels. Line B retained higher protein mass, lower fat mass and greater HP compared to Line A. This was followed by higher feed intake in Line B. Further, Line B exhibited higher EREp and lower EREf across dietary ME levels. In summary, PT homeostasis and body composition changes in broiler lines studied seemed to be regulated by the birds' intent to normalize energy intake as per physiological need by controlling feed intake.

In vivo collagen and mixed muscle protein turnover in 2 meat-type broiler strains in relation to woody breast myopathy

Two meat-type broiler strains, strain A and strain B, were reared in floor pens (25 birds/pen; 45 pens/strain) for pectoralis (P) major collagen and mixed muscle protein turnover (PT) study from 0-56 D using primary breeder nutrition and husbandry guidelines. Forty broilers (n = 10/strain for collagen PT; n = 10/strain for mixed muscle PT) were selected at each sampling age at day 21, 28, 35, 42, and 56 and infused with 1-¹³C proline (Pro) and ¹⁵N-phenylalanine (Phe) which are used as amino acid tracers for collagen and mixed muscle PT measurements, respectively. Muscle and plasma samples were collected, and enrichments of 1-¹³C Pro and ¹⁵N-Phe were determined using mass spectrometry. Fractional synthesis rate (FSR) and fractional degradation rate (FDR) were measured for collagen and mixed muscle using precursor-product principle. At day 42, after separating the sampled broilers as myopathy (woody breast [WB] score > 1) and nonmyopathy (WB = 0), plasma metabolites were screened for differential 3-methyhistidine (3-MH) expression for both strains. Data were analyzed using one-way ANOVA using t test. Results showed that collagen and mixed muscle FSR and FDR in pectoralis major decreased (P < 0.05) for both strains as the broilers aged. FSR for collagen and FDR for mixed muscle were higher for strain B than those for strain A (P < 0.05). Total collagen was higher (P < 0.05) for strain B. Differentially expressed 3-MH in plasma was higher (P < 0.05) for myopathy-affected broilers indicating greater muscle degradation occurring in myopathy-affected broiler types for both strains. 3-MH Expression in plasma was higher for strain B than for strain A. The research findings showing an increased collagen content per unit muscle weight in pectoralis major in strain B (than in strain A) could be due to higher mixed muscle FDR and increased collagen FSR occurring during the grow-out period. The increased degradation of muscle fibers and probable replacement of muscle-specific protein with connective tissue, mainly collagen, was an evident pathophysiological phenomenon occurring in myopathy-affected broilers.

Effects of dietary amino acid levels and ambient temperature on mixed muscle protein turnover in Pectoralis major during finisher feeding period in two broiler lines

Two broiler lines A and B were fed experimental diets from 21 to 42 days with an objective to determine Pectoralis major protein turnover (PT) as affected by the dietary amino acid (AA) levels and ambient temperature. Experimental diets (n = 9 replicate pens per diet) were formulated to 3,150 kcal/kg with five levels of digestible lysine (dLys) -80, 90, 100, 110 and 120% of recommended AA level giving g dlys/Mcal values of 2.53, 2.85, 3.17, 3.48 and 3.80 respectively. All other AA was formulated to a fixed ratio to dLys. Fractional synthesis or degradation rates (FSR or FDR) of P. major were measured on day 36 and day 42 for all dietary treatment levels for both broiler lines using stable isotope of AA (¹⁵ N-phenylalanine) as metabolic tracer. Experimental feeding studies were conducted once in hot season (24-hr mean ~ 85.3°F; 80.9% RH) and repeated in cool season (24-hr mean ~ 71.6°F; 61.7% RH) of the year. The FSR values increased (p < .05) as digestible AA in diet increased for both broiler lines in hot season until break point FSR occurring at 106.2% AA level. The average FSR values measured were higher for Line B at day 36 (20.98%/D for Line B vs. 20.69%/D for Line A) and at day 42 (16.07%/D for Line B vs. 12.47% D for Line A). FDR values observed at day 36 and day 42 were not different between lines (p > .05). Similar trends but elevated values of FSR and FDR in cool season than in hot season were recorded for both the lines. Line B showed the higher mixed muscle protein accretion (%/D) than Line A by actually increasing the FSR which was correlated by higher lean mass deposition and higher feed intake (p < .05). The overall findings indicated that PT response in P. major due to effects of digestible AA levels and ambient temperature was different and line-specific.

Effects of dietary L-arginine levels on small intestine protein turnover and the expression of genes related to protein synthesis and proteolysis of layers

The aim of this study was to test the effects of dietary L-arginine (Arg) levels on protein turnover in the small intestine and the expression of genes related to protein synthesis and proteolysis of laying hens. Xinyang Black commercial laying hens (n = 864, aged 217 d) were randomly distributed to 6 treatments with 4 replicates of 36 birds. The dietary treatments were corn-corn gluten meal based diets containing 0.64, 0.86, 1.03, 1.27, 1.42 and 1.66% L-Arg, respectively. Fractional protein synthesis rate (FSR) and fractional protein gain rate (FGR) in the jejunum were the highest in the 1.27% L-Arg group. The mRNA expression of target of rapamycin (TOR), ribosomal protein S6 kinase 1 (S6K1), and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) in the duodenum reached the highest in the 1.27% L-Arg group, while the mRNA expression of 20S proteasome (20S) was the lowest in the 1.27% L-Arg group. The mRNA abundances of TOR and S6K1 in the jejunum were the highest in the 1.27% L-Arg group, while the mRNA expression of 20S was the lowest in the 1.27% L-Arg group, and the protein expression and phosphorylation levels of TOR in the 1.27% L-Arg group were higher than those in the 0.64% L-Arg group. These results indicate that the action of an appropriate level of dietary L-Arg to improve the protein synthesis of the small intestine involves up-regulating the protein expression and phosphorylation level of TOR in the jejunum accompanied by inhibiting the mRNA expression of 20S of laying hens.

The effect of sexual maturity and egg production on skeletal muscle (pectoralis major and gastrocnemius) protein turnover in broiler breeder pure lines

A study was conducted to evaluate the effect of sexual maturity on pectoralis major and gastrocnemius muscle protein turnover in broiler breeder pure lines. Protein turnover in skeletal muscle tissue was determined in 4 broiler breeder pure lines (Line A, Line B, Line C and Line D) at 22, 27, 33, 37, 44, and 50 wk of age. A completely randomized design with a factorial arrangement 4 × 6 (4 lines and 6 time periods (ages)) was used. There were 5 replicates per line/time and each hen represented a replicate. Five hens/line at each age were given an intravenous flooding-dose of 15N-phenylalanine (150 mM, 40 atom percent excess (APE) at a dose of 10 mL/kg. After 10 min, birds were euthanized using CO2 asphyxiation and the breast and leg muscle excised and snap frozen in liquid nitrogen for protein turnover analysis. Excreta was collected from each breeder for 3-methyl histidine (3-MH) analysis. There was a significant age effect for the breast muscle fractional synthesis rate (FSR), but no main effects (age and line) for leg muscle FSR. The FSR in breast muscle tissue decreased in hens from wk 22 (first egg) to wk 33 (peak egg production). There was a significant age effect on fractional breakdown rate (FBR) in breast and leg muscle. The FBR in breast muscle increased in hens from wk 22 to wk 33 and remained high through wk 37. Breast muscle FBR significantly decreased in hens from wk 37 to wk 50. The FBR in leg muscle tissue increased in hens from wk 33 to wk 37 and then decreased at wk 50. No line effect was seen for FSR or FBR. There is a large increase in skeletal muscle FBR during the transition for the pullet to sexual maturity with increases in skeletal muscle FBR in the breast and leg muscle through peak egg production. Protein turnover in skeletal muscle tissue is believed to be a source of nutrients for egg production.

Practical recommendations for the reduction of memory effects in compound-specific 15N/14N-ratio analysis of enriched amino acids by gas chromatography/combustion/isotope ratio mass spectrometry

Gas chromatography/combustion/isotope ratio mass spectrometry (GC-C-IRMS) is a highly sensitive approach which allows the analysis of the (13)C/(12)C and (15)N/(14)N isotope composition of amino acids in the range of natural abundance or in slightly (13)C- and (15)N-enriched samples. However, the accuracy of measurements remains a permanent challenge. Here we show the effect of the presence of slightly (15)N-enriched compounds in physiological samples on the accuracy and reproducibility of (15)N-abundances of amino acids within or between analytical runs. We spiked several individual amino acids with the respective (15)N-labelled isotopomer and measured the (15)N/(14)N ratios of other amino acids in the same sample or in the following analytical runs. Intra- and inter-run memory effects can be observed in (15)N/(14)N ratios of amino acids. Sample throughput is reduced when cleaning runs using standard mixtures are required to restore initial conditions after runs of samples with (15)N-enriched analytes. Possible reasons for the observed phenomenon and its implications for work in the lower (15)N-enrichment range (<0.5 APE) are discussed and include different aspects of gas chromatography, derivatisation, and hot catalytic metal surface effects. Results need to be interpreted with caution if complex physiological samples contain (15)N-enriched amino acids beyond 500‰ δ(15)N (~0.18 APE).

Fractional protein synthesis rates are similar when measured by intraperitoneal or intravenous flooding doses of L-[ring-2H5]phenylalanine in combination with a rapid regimen of sampling in piglets

Fractional protein synthesis rates (FSR) are widely measured by the flooding dose technique via either an i.g. or an i.v. route. This study was conducted to compare differences in tracer incorporation and FSR in organs and tissues of fed piglets. The piglets were surgically implanted with catheters and randomly assigned to receive a flooding dose of Phe (1.5 mmol/kg body weight, 40 percent molar enrichment with [(2)H(5)]Phe) in saline administered via an i.p. or an i.v. route. [(2)H(5)]Phe free-pool enrichment in plasma increased logarithmically (P < 0.05) from 0 to 25% in the i.p. group, whereas it rose to a peak level within 3 min of the tracer injection and then decreased linearly (P < 0.05) in the i.v. group. Intracellular free-pool tracer enrichments in organs and tissues were within the range of the values measured for the plasma-free pool (25-27%), reaching the flooding status. Administration of the tracer via the i.p. and i.v. routes induced a logarithmical pattern (P < 0.05) of a surge in plasma cortisol concentrations within 30 min. Measurements of FSR in plasma, cardiac muscle, and skeletal muscles were lower (P < 0.05) in the i.p. than in the i.v. group due to the adverse effect of cortisol surge being more dramatic (P < 0.05) in the i.p. than in the i.v. group at 30 min of the post-tracer administration. We conclude that FSR may be measured by the flooding dose through an i.p. or an i.v. route and the i.p. route may underestimate FSR by the flooding dose for plasma, cardiac muscle, and skeletal muscles. This concern may be addressed by a fast regimen of sampling to be completed within 12-20 min after an i.p. route of tracer injection.

Measuring synthesis rates of nitrogen-containing polymers by using stable isotope tracers1,2

The major N-containing polymer compounds in the body include protein, RNA, and DNA. The endogenous gastrointestinal secretions as well as the portal-drained visceral and peripheral immune responses are basic physiological functions. Elevated endogenous secretions and immune activities, as affected by developmental stages, diets, and management factors, decrease the availability of dietary nutrients for peripheral muscle synthesis and deposition. Measurements of in vivo protein, RNA, and DNA synthesis rates associated with the viscera, peripheral immune cells, and skeletal muscles should, in principle, be the sensitive biochemical and cellular endpoints for studying factors affecting nonruminant nutrition, metabolism, and growth. The selection of stable isotope tracers for precursors, routes of tracer delivery, and mass spectrometric analyses of tracer enrichments are the major methodological considerations. To measure in vivo protein, RNA, and DNA synthesis rates, oral feeding with heavy water (2H2O), and continuous infusion of [U-13C]glucose and [15N]Gly intravenously for labeling the sugar moieties ribose and deoxyribose and de novo purine base synthesis have been established. Flooding doses of tracer Phe, for example, L-[ring-2H5]Phe, via the i.p. route are reliable and cost-effective for measuring in vivo protein synthesis rates, especially for the viscera in small nonruminants. Therefore, measurements of the major N-containing polymer synthesis rates in the viscera, the peripheral immune cells, and muscles through oral feeding with 2H2O and/or i.p. flooding doses of Phe tracers are the emerging tools for studying nonruminant nutrition, metabolism, and growth under research and field test conditions.