Dietary Amino Acid Restriction Research Articles

Abstract 10708: Dietary Methionine Restriction Protects Against Abdominal Aortic Aneurysm via Amino Acid Starvation Response

Introduction: Dietary intervention emerges as a promising non-medicinal avenue for the treatment of a wide range of diseases. Limiting the intake of single amino acid has been shown to produce health benefits similar to that of calorie restriction yet without significant risks of malnutrition. One of the established regimen, methionine restriction (MR), was recently shown to confer pleiotropic benefits in cardiometabolic disease models, largely attributed to the activation of the GCN2-mediated amino acid starvation response pathway. However, the therapeutic and mechanistic implications of dietary amino acid restriction remain unknown in abdominal aortic aneurysm (AAA), a lethal vascular disease that is without a cure other than the traumatic surgical repairs. Herein, we sought to probe the outcome of MR as well as the role of GCN2 in AAA. Methods and Results: Following a 2-week pre-treatment with MR (20% methionine level) or iso-caloric control diet, male Sprague Dawley rats were subjected to intraluminal elastase perfusion. At day 7, animals in the MR group showed significantly less aneurysmal dilation in comparison to control. To investigate the contribution from the GCN2-mediated amino acid starvation response, we subjected animals to the same dietary regimen of MR or control, followed by GCN2 silencing in the elastase-challenged aortic segments through localized infusion with GCN2-targeting or scrambled shRNA lentivirus. Indeed, tuning down aortic GCN2 effectively compromised the benefits exerted by MR against AAA. Finally, we determined whether GCN2 constitutes an intrinsic protector against aortic degeneration using GCN2 knockout mice ( Gcn2 -/- ). Following periaortic elastase challenge and β-aminopropionitrile treatment, Gcn2 -/- mice displayed exacerbated expansion of aneurysmal lesions in comparison to Gcn2 +/+ control mice at day 28 post procedure. Conclusions: Our study provides the first experimental evidence supporting a potential role of dietary amino acid restriction (e.g., MR) in the prevention of AAA development. Additionally, GCN2-mediated amino acid starvation response possibly underlies the anti-AAA benefit exerted by MR and serves as an intrinsic protector against AAA pathogenesis.

Dietary lysine restriction induces lipid accumulation in skeletal muscle through an increase in serum threonine levels in rats

We previously reported that dietary amino acid restriction induces the accumulation of triglycerides (TAG) in the liver of growing rats. However, differences in TAG accumulation in individual cell types or other tissues were not examined. In this study, we show that TAG also accumulates in the muscle and adipose tissues of rats fed a low amino acid (low-AA) diet. In addition, dietary lysine restriction (low-Lys) induces lipid accumulation in muscle and adipose tissues. In adjusting the nitrogen content to that of the control diet, we found that glutamic acid supplementation to the low-AA diet blocked lipid accumulation, but supplementation with the low-Lys diet did not, suggesting that a shortage of nitrogen caused lipids to accumulate in the skeletal muscle in the rats fed a low-AA diet. Serum amino acid measurement revealed that, in rats fed a low-Lys diet, serum lysine levels were decreased, while serum threonine levels were significantly increased compared with the control rats. When the threonine content was restricted in the low-Lys diet, TAG accumulation induced by the low-Lys diet was completely abolished in skeletal muscle. Moreover, in L6 myotubes cultured in medium containing high threonine and low lysine, fatty acid uptake was enhanced compared with that in cells cultured in control medium. These findings suggest that the increased serum threonine in rats fed a low-Lys diet resulted in lipid incorporation into skeletal muscle, leading to the formation of fatty muscle tissue. Collectively, we propose conceptual hypothesis that “amino-acid signal” based on lysine and threonine regulates lipid metabolism.

Dietary Essential Amino Acid Restriction Promotes Hyperdipsia via Hepatic FGF21.

Prior studies have reported that dietary protein dilution (DPD) or amino acid dilution promotes heightened water intake (i.e., hyperdipsia) however, the exact dietary requirements and the mechanism responsible for this effect are still unknown. Here, we show that dietary amino acid (AA) restriction is sufficient and required to drive hyperdipsia during DPD. Our studies demonstrate that particularly dietary essential AA (EAA) restriction, but not non-EAA, is responsible for the hyperdipsic effect of total dietary AA restriction (DAR). Additionally, by using diets with varying amounts of individual EAA under constant total AA supply, we demonstrate that restriction of threonine (Thr) or tryptophan (Trp) is mandatory and sufficient for the effects of DAR on hyperdipsia and that liver-derived fibroblast growth factor 21 (FGF21) is required for this hyperdipsic effect. Strikingly, artificially introducing Thr de novo biosynthesis in hepatocytes reversed hyperdipsia during DAR. In summary, our results show that the DPD effects on hyperdipsia are induced by the deprivation of Thr and Trp, and in turn, via liver/hepatocyte-derived FGF21.

Tissue-specific roles of GCN2 in aging and autosomal dominant retinitis pigmentosa

The organisms have the capacity to sense and adapt to their surroundings for their life in a dynamic environment. In response to amino acid starvation, cells activate a rectifying physiological program, termed the integrated stress response (ISR), to restore cellular homeostasis. General controlled non-repressed (GCN2) kinase is a master regulator of the ISR and modulates protein synthesis in response to amino acid starvation. We previously established the GCN2/ATF4/4E-BP pathway in development and aging. Here, we investigated the tissue-specific roles of GCN2 upon dietary restriction of amino acid in a Drosophila model. The knockdown of GCN2 in the gut and fat body, an energy sensing organ in Drosophila, abolished the beneficial effect of GCN2 in lifespan extension upon dietary restriction of amino acids. Proteome analysis in an autosomal dominant retinitis pigmentosa (ADRP) model showed that dietary restriction of amino acids regulates the synthesis of proteins in several pathways, including mitochondrial translation, mitochondrial gene expression, and regulation of biological quality, and that gcn2-mutant flies have reduced levels of these mitochondria-associated proteins, which may contribute to retinal degeneration in ADRP. These results indicate that the tissue-specific regulation of GCN2 contributes to normal physiology and ADRP progression.

Performance and Transcriptional Response of the Green Peach Aphid Myzus persicae to the Restriction of Dietary Amino Acids.

Free amino acids in the phloem sap are the dominant nitrogen source for aphids, but their availability is usually poor. Although some studies have explored the effect of dietary amino acid restriction on aphid performance, little is known about the molecular basis of these effects. Here, we examined the performance and transcriptome of the green peach aphid, Myzus persicae, fed a standard diet (Control diet) or a diet containing 50% of the total amino acids of the Control diet (Half diet). Aphid weight and fecundity were significantly reduced in the Half diet group. Transcriptomic analysis showed that a total of 1460 genes were differentially expressed between the groups were fed on the two diets, which many of them were associated with nutrient and energy metabolism. When feeding on the Half diet, aphids upregulated genes associated with the amino acid biosynthetic pathway (predominantly amino acid biosynthesis genes and some amino acid transporter genes) as well as the cysteine and serine protease genes. Furthermore, these aphids displayed increased expression of genes associated with glycolysis, which could generate intermediates for de novo amino acid biosynthesis. Consistent with this, elevated glucose levels were observed in aphids in the Half diet group. Additionally, the expression levels of several genes associated with hormonal signaling pathway were altered. Several genes related to juvenile hormone and insulin-like peptide (ILP) signaling were downregulated, including Krüppel homolog 1 (Kr-h1) and insulin-like peptide 5 (Ilp5), respectively. In contrast, several genes related to ecdysone signaling were upregulated including broad-complex core protein (Br-c) and shade (Shd). Despite their poor performances, M. persicae adapted to dietary restriction of amino acids, through upregulation of genes involved in amino acid biosynthesis, glycolysis, and protein degradation, as well as by altering the expression level of genes involved in hormone signaling pathways.

Early dietary amino acid restrictions and flaxseed oil supplementation on the leanness of pigs and quality of pork: Growth performance, serum metabolites, carcass characteristics, and physical and sensory characteristics of pork

A total of 64 pigs (Yorkshire) were used to investigate the effect of early dietary amino acid (AA) restrictions [100 or 80% of the 2012 NRC standardized ileal digestible (SID) Lys requirements during the grower and finisher-1 phases] and flaxseed oil supplementation [0 or 3% (+2% poultry fat)] in a 2×2 factorial arrangement of treatments on grower-finisher pigs. At 24.7±0.5kg body weight (BW), pigs were randomly assigned to 4 grower diets with 4 gilt and 4 castrated male pens/treatment and 2 gilts or 2 castrated males/pen, and switched to fnisher-1 diets when they reached 51.2±0.3kg. Pigs were offered common finisher-2 diets after 80.0±0.4kg, and those received 0 or 5% lipids during the grower and finisher-1 phases were continued to receive 0 or 5% lipids. Ultrasound backfat measurements and blood samples were collected at the end of the grower, finisher-1, and finisher-2 phases, and pigs were harvested at 110.5±0.5kg to assess carcass traits and physical and sensory characteristics of pork. During the grower phase, although pigs consumed less feed, SID Lys, and digestible energy (DE; P<0.015), their average daily BW gain was not really depressed by the dietary AA restrictions. During the finisher-1 phase, however, pigs fed the AA restricted diets had greater BW gain (P=0.042) and utilized SID Lys more efficiently (P<0.001) for BW gain than those fed the unrestricted diets. Pigs fed the diets supplemented with lipids had lower feed intake (P=0.007) but greater BW gain (P =0.03) during the grower phase, and their BW gain:feed (P<0.045) was improved during the all phases of production. Overall BW gain was not affected by the early dietary AA restrictions, but overall efficiency of feed, SID Lys, or DE utilization for BW gain (P<0.005) was improved by the AA restrictions. Similarly, the early dietary AA restrictions had no effect on fat-free lean (FFL) gain but increased FFL gain:SID Lys (P<0.001) and tended to increase FFL gain:DE (P=0.095). Serum urea-N (P<0.026) at the end of the grower and finisher-1 phases was reduced, and serum glucose (P=0.027) at the end of the grower phase was increased by the dietary AA restrictions. The dietary lipids tended to increase and increased serum triglycerides at the end of the grower (P=0.075) and finisher-1 and 2 (P<0.018) phases, respectively, and reduced urea-N (P=0.037) at the end of the finisher-2 phase. At the end of the finisher-1 phase, the dietary lipids increased serum cholesterol in pigs fed the unrestricted diet but had no effect on those fed the AA restricted diet (AA restrictions x lipid supplementation, P=0.029). The dietary AA restrictions tended to reduce the initial tenderness (P<0.057) and reduced flavor intensity (P=0.048) of pork slightly. Belly firmness (P<0.001) was reduced and off-flavor (P=0.007) was increased slightly by the dietary lipids. There was no effect of dietary treatments on ultrasound backfat. In conclusion, the dietary lipids improved BW gain:feed but reduced belly firmness and increased off-flavor slightly. The dietary AA restrictions had no effect on overall BW gain or FFL gain but improved overall efficiency of AA and DE utilization for BW gain and FFL gain.

4E-BP is a target of the GCN2-ATF4 pathway during Drosophila development and aging.

Reduced amino acid availability attenuates mRNA translation in cells and helps to extend lifespan in model organisms. The amino acid deprivation-activated kinase GCN2 mediates this response in part by phosphorylating eIF2α. In addition, the cap-dependent translational inhibitor 4E-BP is transcriptionally induced to extend lifespan in Drosophila melanogaster, but through an unclear mechanism. Here, we show that GCN2 and its downstream transcription factor, ATF4, mediate 4E-BP induction, and GCN2 is required for lifespan extension in response to dietary restriction of amino acids. The 4E-BP intron contains ATF4-binding sites that not only respond to stress but also show inherent ATF4 activity during normal development. Analysis of the newly synthesized proteome through metabolic labeling combined with click chemistry shows that certain stress-responsive proteins are resistant to inhibition by 4E-BP, and gcn2 mutant flies have reduced levels of stress-responsive protein synthesis. These results indicate that GCN2 and ATF4 are important regulators of 4E-BP transcription during normal development and aging.

Effect of severe amino acid restriction on subsequent growth performance and urinary N excretion in growing pigs

Using 12 gilts (initial body weight: 38.4±1.1kg), we investigated an effect of early dietary amino acid (AA) restrictions on daily changes in urinary N excretion and growth performance during the following re-alimentation period. After the 10-d preliminary period of using a high-protein diet, we estimated protein deposition rate (PD) of pigs, two 14-d experimental periods followed. Pigs were allotted to 2 groups so as the mean PD of both groups was similar. During the first 14-d restriction period, the control group was fed an AA adequate diet, while the restricted group was fed an AA deficient diet. During the following 14-d re-alimentation period, both groups were fed AA adequate diet. Starting on d 12 of the restricted period, samples of urine were collected from both groups using permanent bladder catheters to monitor daily N excretion. Pigs were weighed weekly, the remaining feed were collected daily, and average daily feed intake (ADFI), average daily gain (ADG), gain:feed (G:F) were calculated for each period separately and overall for the restriction and re-alimentation periods. For the same periods, urinary N excretion rate was determined. During the re-alimentation period, pigs that were previously fed the AA deficient diet tended (P=0.060) to have greater ADFI (2297 vs. 2171g/d), and greater (P<0.05) ADG (1216 vs. 827g/d) and G:F (529 vs. 379g/kg) than the control group. There were no differences in urinary N excretion between the restricted (20.8g/d) and control (21.2g/d) groups. During the overall period, lower (P<0.05) ADG (643 vs. 817g/d) and G:F (294 vs. 381g/kg) were observed in the restricted group compared with the control group. There was lower urinary N excretion in the restricted group in comparison to the control group as a result of early dietary AA restrictions. After early dietary AA restrictions, pigs demonstrated compensatory response in growth performance, but reduction in urinary N excretion was observed for only a short-term. During the overall period, including the restriction and re-alimentation period, compensatory growth was not observed, and lower urinary N excretion was resulted from early dietary AA restrictions. Compensatory response was not strong enough to offset the differences caused by severe early dietary AA restrictions.

Amino acid sensing in dietary-restriction-mediated longevity: roles of signal-transducing kinases GCN2 and TOR

DR (dietary restriction), or reduced food intake without malnutrition, is associated with extended longevity, improved metabolic fitness and increased stress resistance in a wide range of organisms. DR is often referred to as calorie restriction, implying that reduced energy intake is responsible for its widespread and evolutionarily conserved benefits. However, recent data indicate dietary amino acid restriction as a key mediator of DR benefits. In fruitflies, an imbalance in essential amino acid intake is thought to underlie longevity benefits of DR. In mammals, reduced dietary protein or essential amino acid intake can extend longevity, improve metabolic fitness and increase stress resistance. In the present paper we review two evolutionarily conserved signal transduction pathways responsible for sensing amino acid levels. The eIF2α (eukaryotic initiation factor 2α) kinase GCN2 (general amino acid control non-derepressible 2) senses the absence of one or more amino acids by virtue of direct binding to uncharged cognate tRNAs. The presence of certain amino acids, such as leucine, permits activation of the master growth regulating kinase TOR (target of rapamycin). These two signal transduction pathways react to amino acid deprivation by inhibiting general protein translation while at the same time increasing translation of specific mRNAs involved in restoring homoeostasis. Together, these pathways may contribute to the regulation of longevity, metabolic fitness and stress resistance.

Effect of the degree and duration of early dietary amino acid restrictions on subsequent and overall pig performance and physical and sensory characteristics of pork1

The objective of this study was to investigate the effect of the degree and duration of early dietary AA restrictions on subsequent and overall pig performance and physical and sensory characteristics of pork. For the grower (G) and finisher-1 (F1) phases, 3 corn-soybean meal diets were formulated to contain 100, 80, or 60% of the 1998 NRC total Lys recommendations (100G, 80G, or 60G, and 100F1, 80F1, or 60F1, for the G and F1 phases, respectively). For the finisher-2 (F2) phase, a common corn-soybean meal diet was formulated to satisfy the 1998 NRC total Lys recommendation. Thirty gilts and 30 castrated males (2 gilts or 2 castrated males/pen) were randomly assigned to 5 dietary treatments (100G-100F1, 80G-100F1, 80G-80F1, 60G-100F1, and 60G-60F1) when BW was 22.7 +/- 0.3 kg. Pigs were switched to F1 and F2 diets at 50.7 +/- 0.4 and 79.9 +/- 0.5 kg of BW, respectively. Pigs had ad libitum access to feed and water. All pigs were slaughtered at 110.7 +/- 0.5 kg of BW, and LM samples were collected. Pigs fed the 60G diet had less (P < or = 0.05) ADG during the G phase and greater (P < or = 0.05) ultrasound backfat (UBF) at the end of the G phase than those fed the 100G diet. The ADG decreased linearly (R(2) = 0.70; P < 0.001) as the degree of AA restrictions became more severe. Although serum total protein (TP) and albumin concentrations in pigs fed the 60G-100F1 diets were less (P < or = 0.05) than those fed the 100G-100F1 diets at the end of the G phase, TP concentration was similar between the 2 groups at the end of the F1 phase. Likewise, ADG during the F1 phase and UBF at the end of the F1 phase in pigs fed the 60G-100F1 diets were similar to those fed the 100G-100F1 diets. Feeding the 80G diet resulted in numerically decreased ADG during the G phase, but there was no difference in ADG during the F1 and F2 phases or UBF at the end of F1 and F2 phases between pigs fed the 80G and 100G diets. Overall, pigs fed the 80G-80F1 diets had similar ADG, but less (P < or = 0.05) fat-free lean gain (LG) than those fed the 100G-100F1 diets. These pigs also had less (P < or = 0.05) serum TP and albumin concentrations than pigs fed the 100G-100F1 diets throughout the study. Pigs fed the 60G-60F1 diets had less (P < or = 0.05) overall ADG and G:F and less (P < or = 0.05) LM area and LG than those fed the 100G-100F1 diets. However, they had a greater (P < or = 0.05) subjective marbling score than those fed the 100G-100F1 diets. The results indicated that pigs fed the 80G-80F1 diets may have exhibited compensatory growth in BW gain, but not in terms of lean accretion. Growth performance and carcass traits of pigs fed the 60G-60F1 diets were reduced, indicating that the restriction may have been too severe or too long or both. Early dietary AA restrictions had no clear effect on physical and sensory characteristics of pork.

Efecto de la restricción de aminoácidos excepto la metionina sobre el estrés oxidativo mitocondrial

Introduction Protein or methionine restriction in the diet is known to decrease reactive oxygen species (ROS) production and mitochondrial oxidative stress and to increase maximum longevity in rodents, which could explain how these changes also take place in dietary restriction. However, it is not known whether restriction of other amino acids is also involved. To clarify this question, we studied the effect of restricting all the amino acids, except methionine, of the semi-purified diet, AIN 93G, in Wistar rats. Material and methods Seven-week old male Wistar rats (n=16) were randomly divided into two groups: a control group and a group with 40% restriction of dietary amino acids except methionine. After 7 weeks of dietary treatment, the animals were sacrificed and their livers were extracted to isolate mitochondria immediately and measure ROS production and oxygen consumption; these data allowed the percentage of free radical leak to be calculated. Oxidative damage to mitochondrial DNA was calculated as 8-oxo-7,8-dihydro-2′-deoxyguanosine by HPLC-EC. Results At the end of the experimental period, a decrease in kidney weight was observed, but the weight of the liver, heart and brain was unchanged. ROS production in isolated liver mitochondria was unchanged with complex I (pyruvate/malate or glutamate/malate) or complex II (succinate) linked substrates. Maximum rates of ROS production significantly decreased with glutamate/malate+rotenone but not with pyruvate/malate+rotenone or with succinate. There were no changes in oxygen consumption with any substrate either in state 4 (resting) or in state 3 (phosphorylating). In agreement with the ROS production results, there were no differences between groups in oxidative damage to mitochondrial DNA. Conclusions Taken together with previous results concerning methionine restriction, the results obtained in the present study clearly show that the decrease in ingestion of only one molecule, methionine, causes the decrease in ROS production and oxidative damage to mitochondrial DNA that is observed in dietary restriction in relation to the decrease in the rate of aging.

Effect of 40% restriction of dietary amino acids (except methionine) on mitochondrial oxidative stress and biogenesis, AIF and SIRT1 in rat liver

Previous studies have shown that the decrease in mitochondrial reactive oxygen species (mitROS) generation and oxidative damage to mitochondrial DNA (mtDNA) that occurs during life extending dietary restriction also occurs during protein or methionine restriction, whereas it does not take place during carbohydrate or lipid restriction. In order to study the possible effects of other amino acids, in this investigation all the dietary amino acids, except methionine, were restricted by 40% in male Wistar rats (RESTAAS group). After 6-7 weeks, experimental parameters were measured in the liver. Amino acid restriction did not change the levels of the methionine metabolites S-adenosylmethionine and S-adenosylhomocysteine, mitochondrial oxygen consumption and ROS generation, oxidative damage to mtDNA, amounts of the respiratory complexes I-IV, and the mitochondrial biogenesis factors PGC-1alpha and NRF-2. On the other hand, adenylate energy charge, mitochondrial protein oxidation, lipooxidation and glycooxidation, the degree of mitochondrial fatty acid unsaturation, and the amount of the apoptosis inducing factor (AIF) were decreased in the RESTAAS group. Amino acid restriction also increased SIRT1 protein. These results, together with previous ones, strongly suggest that the decrease in mitROS generation and oxidative damage to mtDNA that occurs during dietary restriction is due to restriction of a single aminoacid: methionine. They also show for the first time that restriction of dietary amino acids different from methionine decreases mitochondrial protein oxidative modification and AIF, and increases SIRT1, in rat liver.

Effect of early dietary amino acid restrictions on serum metabolites in pigs selected for lean growth efficiency

Thirty-two select line pigs for lean growth efficiency and 32 control line pigs (average 20 kg) were used in each of the two experiments to assess the effect of dietary amino acid restrictions during the grower phase on serum cholesterol, triglycerides, total protein, albumin, and glucose concentrations. In each experiment, 16 pens with two gilts and 16 pens with two castrated males per pen were assigned within the genetic line to grower (6.1 or 11.1 g lysine kg-1) and finisher diets (6.1 or 8.9 g lysine kg-1) in a 2 × 2 × 2 factorial arrangement in exp. 1, or grower diets (5.0, 7.0, 9.0, or 11.0 g lysine kg-1) in a 2 × 4 factorial arrangement of treatments in exp. 2. Pigs were offered common finisher diets in exp. 2. Serial blood samples were collected in both experiments. Serum cholesterol at the end of the grower phase was greater in the select line pigs in exp. 1 (P = 0.009) and pigs fed diets low in amino acids in exp. 2 (P = 0.005, 0.026, and 0.039 for linear, quadratic, and cubic, respectively). Serum cholesterol was correlated negatively with lysine intake (r = -0.38; P = 0.039) and serum urea nitrogen (r = -0.39; P = 0.032) in exp. 1 and positively with ultrasound backfat (r = 0.78; P = 0.001) in exp. 2. Serum cholesterol, however, may not reflect the cholesterol content of tissues or pork, except liver. At the end of the grower phase, pigs fed grower diets high in amino acids had greater serum total protein in exp. 2 (P = 0.040 and 0.093 for linear and quadratic, respectively) and albumin concentrations in exp. 1 (P = 0.001) and exp. 2 (linear, P = 0.001), and, at the end of the finisher phase, they had greater serum albumin in exp. 1 (P = 0.001) and seemed to have more total protein in exp. 2, even though there was a trend for the grower diet × genotype interaction (P = 0.095). The carryover effects of the grower diet during the realimentation phase seem to be contrary to the expected positive metabolite status of pigs exhibiting compensatory growth after a period of early dietary amino acid restrictions. On the other hand, higher serum total protein in exp. 2 (P = 0.041 and 0.001 at the end of the grower and finisher phases, respectively) and albumin concentrations at the end of the finisher phase in exp. 1 (P = 0.016) and exp. 2 (P = 0.059) in pigs selected for lean growth efficiency may be an indication that pigs utilized amino acids more efficiently for growth and protein accretion. Exploring fully the effect of dietary manipulations and genotypes on serum metabolites is obviously important, and the results of the present research may contribute to the development of the environmentally friendly, optimal feeding strategies for successful and sustainable pig production. Key words: Amino acid restrictions, genotypes, pigs, serum metabolites

Compensatory growth and nitrogen balance in grower-finisher pigs.

Sixteen castrated male pigs (averaging 21.2 +/- 4.9 kg) were used in two trials to investigate the effect of dietary amino acid content during the grower phase on growth performance and N balance. In each trial, pigs were assigned randomly to corn-soybean meal grower diets formulated to contain 5.0 or 11.0 g lysine/kg (as-fed basis). Common Finisher 1 and 2 diets were offered when pigs reached 51.2 +/- 3.3 and 79.5 +/- 3.4 kg, respectively. Pigs were placed in metabolism crates for a 9-d period during each of the grower, Finisher 1, and Finisher 2 phases when they weighed 43.3 +/- 3.9, 70.4 +/- 4.9, and 90.5 +/- 3.8 kg, respectively, to determine N balance. Blood samples were taken from each pig periodically after an overnight fast. Pigs were allowed ad libitum access to feed and water, except during the three adaptation/collection periods. There were no diet x trial interactions; thus, the data were combined. Pigs fed the low-amino acid grower diet grew more slowly and less efficiently (P < 0.001) during the grower phase and had more ultrasound backfat (P = 0.010) at the end of the grower phase than those fed the high-amino acid grower diet. During the Finisher 1 phase, however, pigs fed the low-amino acid diet grew more efficiently (P = 0.012) than those fed the high-amino acid diet, and the grower diet had no effect on overall weight gain, carcass traits, lean accretion, or meat quality scores. Although pigs fed the low-amino acid diet had less serum urea N (P < 0.001) and more glucose (P = 0.009) at 43.3 kg, there seemed to be no clear, long-term effect of the grower diet on serum metabolites. During the grower phase, pigs fed the high-amino acid diet consumed more N (P < 0.001), had higher apparent N digestibility (P = 0.041), N utilization (P = 0.027), and N retention (P < 0.001), and excreted more fecal (P = 0.034) and urinary (P < 0.001) N than those fed the low-amino acid diet. Pigs fed the low-amino acid grower diet, however, had a higher N utilization (P = 0.024) during the Finisher 1 phase, and excreted less urinary N during both the Finisher 1 (P = 0.029) and 2 (P = 0.027) phases than those fed the high-amino acid grower diet. These results indicate that pigs subjected to early dietary amino acid restrictions compensated completely and decreased N excretion during both the restriction and realimentation phases. Compensatory growth can, therefore, have a positive effect not only on the overall efficiency of pig production but also on environment.

Degree of amino acid restrictions during the grower phase and compensatory growth in pigs selected for lean growth efficiency1

A total of 32 select line (SL) and 32 control line (CL) Duroc pigs were used in two trials to determine the effect of dietary amino acid contents during the grower (G) phase and selection for lean growth efficiency on growth performance, carcass traits, and meat quality. In each trial, pigs weighing 20 kg were assigned to 16 pens with two gilts or two castrated males per pen, and pens were randomly assigned within the genetic line to corn-soybean meal G diets formulated to contain 5.0, 7.0, 9.0, or 11.0 g lysine/kg. After 50 kg, all pigs were fed common finisher 1 (F1) and finisher 2 (F2) diets. Pigs were allowed ad libitum access to feed and water. After the initial statistical analyses, the data sets from the two trials were combined. During the G phase, pigs consumed less feed [linear (Ln), P < 0.001] and more lysine (Ln, P < 0.001), grew faster (Ln, P < 0.05) but utilized feed more and lysine less efficiently (Ln, P < 0.001) for weight gain as the amino acid content of G diets increased. Increasing dietary amino acids resulted in less ultrasound backfat (Ln, P < 0.001) and more serum urea nitrogen [Ln, P < 0.001; quadratic (Qd), P < 0.01] at the end of the G phase. Pigs grew more slowly during the F1 (Ln, P < 0.01 and Qd, P = 0.05) and F2 (Ln, P = 0.07) phases and utilized feed and lysine less efficiently (Ln, P < 0.05) for weight gain during the F1 phase as the amino acid content of G diets increased. The grower diet had no effect on overall weight gain and feed efficiency, carcass traits, or meat quality scores. The efficiency of lysine utilization for overall weight gain (Ln, P < 0.001) and lean accretion (Ln, P < 0.05) improved as the amino acid content of G diets decreased. The SL pigs grew faster (P < 0.05) and had less (P < 0.001) ultrasound backfat throughout the study compared with the CL pigs. The SL pigs had less 10th rib backfat (P < 0.001) and tended to have larger longissimus muscle area (P = 0.09) than the CL pigs, which were reflected in greater rate (P < 0.001) and efficiency (P < 0.05) of lean accretion. Marbling (P < 0.05) and meat color (P = 0.07) scores were lower in the SL pigs. No grower diet × genotype interactions were observed in response criteria of interest. The results indicate that pigs subjected to dietary amino acid restrictions during the G phase (as low as 5.0 g lysine/kg) compensated completely in terms of growth rate and body composition regardless of the genotype. Compensatory growth can have a positive impact not only on the overall efficiency of pig production but also on the environment by reducing excretion of unused nutrients.

Degree of amino acid restrictions during the grower phase and compensatory growth in pigs selected for lean growth efficiency.

A total of 32 select line (SL) and 32 control line (CL) Duroc pigs were used in two trials to determine the effect of dietary amino acid contents during the grower (G) phase and selection for lean growth efficiency on growth performance, carcass traits, and meat quality. In each trial, pigs weighing 20 kg were assigned to 16 pens with two gilts or two castrated males per pen, and pens were randomly assigned within the genetic line to corn-soybean meal G diets formulated to contain 5.0, 7.0, 9.0, or 11.0 g lysine/kg. After 50 kg, all pigs were fed common finisher 1 (F1) and finisher 2 (F2) diets. Pigs were allowed ad libitum access to feed and water. After the initial statistical analyses, the data sets from the two trials were combined. During the G phase, pigs consumed less feed [linear (Ln), P < 0.001] and more lysine (Ln, P < 0.001), grew faster (Ln, P < 0.05) but utilized feed more and lysine less efficiently (Ln, P < 0.001) for weight gain as the amino acid content of G diets increased. Increasing dietary amino acids resulted in less ultrasound backfat (Ln, P < 0.001) and more serum urea nitrogen [Ln, P < 0.001; quadratic (Qd), P < 0.01] at the end of the G phase. Pigs grew more slowly during the F1 (Ln, P < 0.01 and Qd, P = 0.05) and F2 (Ln, P = 0.07) phases and utilized feed and lysine less efficiently (Ln, P < 0.05) for weight gain during the F1 phase as the amino acid content of G diets increased. The grower diet had no effect on overall weight gain and feed efficiency, carcass traits, or meat quality scores. The efficiency of lysine utilization for overall weight gain (Ln, P < 0.001) and lean accretion (Ln, P < 0.05) improved as the amino acid content of G diets decreased. The SL pigs grew faster (P < 0.05) and had less (P < 0.001) ultrasound backfat throughout the study compared with the CL pigs. The SL pigs had less 10th rib backfat (P < 0.001) and tended to have larger longissimus muscle area (P = 0.09) than the CL pigs, which were reflected in greater rate (P < 0.001) and efficiency (P < 0.05) of lean accretion. Marbling (P < 0.05) and meat color (P = 0.07) scores were lower in the SL pigs. No grower diet x genotype interactions were observed in response criteria of interest. The results indicate that pigs subjected to dietary amino acid restrictions during the G phase (as low as 5.0 g lysine/kg) compensated completely in terms of growth rate and body composition regardless of the genotype. Compensatory growth can have a positive impact not only on the overall efficiency of pig production but also on the environment by reducing excretion of unused nutrients.

Impact of amino acid nutrition during lactation on body nutrient mobilization and milk nutrient output in primiparous sows.

The impact of amino acid nutrition during lactation on body nutrient mobilization and milk nutrient output in primiparous sows was evaluated. Thirty-six sows, nursing litters of 13 pigs, were allocated daily 6 kg of a fortified corn-soybean meal diet containing a high (HP, 1.20% lysine) or low (LP, .34% lysine) protein content during a 23-d lactation. Dietary lysine concentration was achieved by altering the ratio of corn and soybean meal in the diet. The LP sows consumed less daily ME (14.2 vs 16.1 Mcal; P < .11) and daily lysine (16 vs 59 g; P < .01) than the HP sows. Daily litter weight gain was less (P < .01) for sows fed the LP vs HP diet, and the differences increased (P < . 01) as lactation progressed. The lower litter weight gain for the LP sows was reflective of the lower (P < .01) estimated milk DM, CP, and GE output of these sows. The LP sows lost more body weight (1.23 vs .21 kg/d; P < .01) during the initial 20 d of lactation. In the LP sows, 59% of the weight loss was protein, water, and ash, and 37% was fat. Weight loss in the HP sows was entirely accounted for by body fat mobilization, because these sows accrued body protein, water, and ash. Muscle myofibrillar breakdown rate was higher in LP sows than in HP sows (4.05 vs 2.80%/d; P < .01). On the basis of these data, dietary amino acid restriction during lactation increases maternal mobilization of proteinaceous tissue and reduces milk nutrient output. Maternal protein mobilization is maintained over the entire lactation even though milk output is decreased as lactation progresses.

Growth performance and carcass traits of pigs subjected to marginal dietary restrictions during the grower phase.

Sixty-four individually housed pigs were used to investigate the effect of amino acid content of finisher diets on growth performance of pigs subjected to marginal dietary amino acid restrictions (80% of the 1988 NRC lysine recommendation) during the grower phase. In each of the two trials, low- and high-amino-acid grower diets (.421 and .765 g lysine/MJ DE, respectively) and four finisher diets (.421, .516, .612, and .707 g lysine/MJ DE) were randomly assigned within sex to 16 gilts and 16 castrated males weighing 23.0 +/- 2.0 kg in a 2 x 4 factorial arrangement of treatments. The average weight of pigs after a completion of diet change was 50.4 +/- 2.1 kg. All pigs were slaughtered at an average weight of 105.2 +/- 4.1 kg. Ultrasound backfat thickness was measured at the time of diet change and before slaughter. Pigs were allowed ad libitum access to feed and water. During the grower phase, pigs fed the high-amino-acid diet grew faster (P < .001) and more efficiently (P < .001) and had less ultrasound backfat (P < .001) than those fed the low-amino-acid diet. The grower diet had no effect on weight gain during the finisher phase. Consequently, pigs fed the high-amino-acid grower diet had better overall weight gain (P < .01) than those fed the low-amino-acid diet. The rate of lean accretion was, however, similar between the two groups of pigs. Furthermore, pigs fed the low-amino-acid grower diet seemed to have better carcass quality, as indicated by less ultrasound backfat (P < .01) and larger carcass longissimus muscle area (P < .05). Average and 10th rib carcass backfat decreased linearly (P < or = .05) and lean accretion rate improved linearly (P < .05) as the amino acid content of finisher diets increased, but there was no grower x finisher diet interaction in these and other response criteria. Although no evidence of compensatory weight gain was observed, it is possible that compensatory lean tissue growth may have occurred in pigs subjected to early amino acid restrictions at the expense of fatty tissue growth.

Dietary Restriction of Tyrosine and Phenylalanine: Inhibition of Metastasis of Three Rodent Tumors&lt;xref ref-type="fn" rid="FN2"&gt;2&lt;/xref&gt;

The effects of a combined dietary restriction of tyrosine and phenylalanine on metastasis were investigated with the use of 3 rodent tumor cell lines: B16-bladder 6 (BL6) melanoma inoculated into (C57BL/6 X DBA/2)F1 mice, Lewis lung (3LL) carcinoma inoculated into C57BL/6 mice, and RT7-4bs hepatocarcinoma inoculated into BD-IV rats. When examined for effects on spontaneous metastasis, dietary restriction of tyrosine and phenylalanine had no effect on metastasis to draining lymph nodes in either BL6 or 3LL tumors. However, the restriction did reduce metastasis of RT7-4bs cells to draining lymph nodes by 60%. In all tumor systems, the dietary restriction effectively inhibited the subsequent growth of lymph node tumors. The most marked effect of the dietary restriction was on spontaneous hematogenous metastasis, which was almost totally blocked for BL6 cells and was reduced by 85% for RT7-4bs cells. Tumor-associated splenomegaly also was completely inhibited in 3LL tumor-bearing mice. The selective dietary amino acid restriction failed to reduce initial lung colonization in the experimental metastasis assay but clearly inhibited subsequent tumor outgrowth in the lungs. These findings demonstrate that modification of host nutritional status by restriction of the dietary intake of tyrosine and phenylalanine exerts a dramatic antimetastatic effect directed particularly on spontaneous hematogenous metastasis. Although the preliminary data suggest a primary modulating effect on tumor cell populations growing in diet-restricted animals to reduce inherent metastatic ability, the actual mechanisms remain to be defined.