Effect of amino acid imbalance on the fate of the limiting amino acid

Estimating Amino Acid Requirements in Real-Time for Precision-Fed Pigs: The Challenge of Variability among Individuals

Simple Summary

Precision feeding considers the difference in amino acid requirements among pigs and over time by providing daily tailored diets. This practice allows improving environmental and economic performances. Future systems should focus on maximizing nutrient use efficiency to move towards “green” pig production. This study explored a new method of providing amino acids to maximize their use, mainly focusing on understanding variations in the protein metabolism response among individuals to minimize variation in growth response. This study showed that even pigs fed the same amino acid level might use these nutrients differently, especially in protein deposition. Logically, pigs with the greatest protein deposition are the ones that use amino acids the most efficiently, thus exhibiting the lowest nitrogen excretion. This study helped identify some of the factors affecting the efficiency of nitrogen use in pigs. By improving the understanding of pigs’ nutrient response, pig production can become more resource-efficient.

Abstract

This study aimed to measure protein deposition (PD) in pigs fed with daily tailored diets where either dietary lysine (Lys) or threonine (Thr) were provided at independent levels (ignoring an ideal ratio). A total of 95 growing pigs (35 kg body weight (BW)) with electronic ear tags granting them access to automatic feeders were randomly assigned to treatments. The setup was an unbalanced 2 × 5 factorial arrangement with Lys and Thr provided at five levels (i.e., 60%, 80%, 100%, 120%, and 140% of the estimated individual requirements of Lys and Thr), resulting in 25 treatments for 21 days. The observed PD variation to Lys and Thr provisions was large, with Lys and Thr intake explaining only 11% of the variation. Cluster analysis discriminated pigs with low (167 g/d, n = 16), medium (191 g/d, n = 38), and high (213 g/d, n = 37) PD, but with a similar amino acid intake. Differences in PD were associated with differences in nutrient efficiency of utilization. Providing Lys and Thr in a factorial mode, ignoring an ideal ratio, did not decrease the variability in PD. Future research efforts should focus on identifying and investigating the sources of interindividual variability—a necessary step before final recommendations can be made for AA in precision-fed pigs.

Feeding behavior of growing and finishing pigs fed different dietary threonine levels in a group-phase feeding and individual precision feeding system

Feeding behavior is an important aspect of pig husbandry as it can affect protein deposition (PD) in pigs. A decrease in plasma threonine (Thr) levels may influence feed intake (FI) due to amino acid imbalance. We set out to study whether different Thr inclusion rates of 70%, 85%, 100%, 115%, and 130% of the ideal Thr:lysine (Lys) ratio of 0.65 in two different feeding programs (individual precision feeding and group-phase feeding could affect pig feeding behavior and consequently PD. Two 21-d trials were performed in a 2 × 5 factorial setup (feeding systems × Thr levels) with 110 pigs in the growing phase [25.0 ± 0.8 kg of body weight (BW)] and 110 pigs in the finishing phase (110.0 ± 7.0 kg BW), which correspond to 11 pigs per treatment in each trial. Pigs were housed in the same room and fed using computerized feeding stations. The total lean content was estimated by dual x-ray absorptiometry at the beginning (day 1) and the end (day 21) of the trial. Multivariate exploratory factor analysis was performed to identify related variables. Confirmatory analysis was performed by orthogonal contrasts and Pearson correlation analysis. Graphical analysis showed no difference in feeding patterns between feeding systems during the growing or finishing phase. Pigs exhibited a predominant diurnal feeding, with most meals (73% on average) consumed between 0600 and 1800 h. Exploratory factor analysis indicated that feeding behavior was not related to growth performance or PD in growing or finishing pigs. Changes in feeding behavior were observed during the growing phase, where increasing dietary Thr resulted in a linear increase in the FI rate (P < 0.05). During the finishing phase, the duration of the meal and FI rate increased linearly as dietary Thr increased in the diet (P < 0.05). These changes in feeding behavior are, however, correlated to BW. In conclusion, the exploratory factor analysis indicated that feeding behavior had no correlation with growth performance or protein and lipid deposition in growing or finishing pigs. Dietary Thr levels and feeding systems had no direct effect on FI.

Phenylalanine hydroxylase activity and expression in chicks subjected to phenylalanine imbalance or phenylalanine toxicity

Experiments were performed to investigate the activity of hepatic Phe hydroxylase (PAH) and plasma amino acid concentrations under conditions of Phe imbalance or toxicity in chicks fed on experimental diets from 7 to 14 or 16 d of age. In experiment 1, Phe imbalance was created by adding 10% of a mixture of indispensable amino acids lacking Phe (IAA - Phe) to a basal diet containing 0.46% Phe. The activity of PAH was not significantly affected by the imbalance. Correcting the imbalance by adding 1.12% Phe to the diet prevented the growth impairment and increased the activity of PAH. In experiment 2, growth was reduced by the addition of excess (2%) Phe to the basal diet. Correcting the excess by adding the IAA - Phe to the diet prevented the growth reduction. The activity of PAH was not significantly affected by 2% Phe, but it increased in chicks fed the corrected diet. The levels of PAH mRNA were not affected by the dietary treatments. A factorial arrangement of treatments with 3 dietary levels of Phe (0.46, 1.58, and 2.46%) with or without the IAA - Phe was used in experiment 3. The effects on growth were similar to those of the same treatments in experiments 1 and 2. The addition of Phe significantly increased hepatic PAH activity, but there was no detectable main effect of the IAA - Phe and no interaction. Plasma Phe concentration was increased by dietary Phe and decreased by the IAA - Phe mixture. We conclude that hepatic PAH activity in chicks variably increases in response to Phe or a 10% dietary supplement of indispensable amino acids including Phe but does not increase in response to IAA - Phe when the amino acids are added to a diet that is marginally adequate in Phe. The increased activity does not involve changes in PAH mRNA. The effects of IAA - Phe on plasma Phe concentrations appear to be independent of hepatic PAH activity as measured in vitro.

Regulation of cationic amino acid transport: the story of the CAT-1 transporter

The discovery of the function of the receptor for the ecotropic retrovirus as a membrane transporter for the essential amino acids lysine and arginine was a landmark finding in the field of molecular nutrition. This finding indicated that cationic amino acid transporters (CATs) act pathologically as viral receptors. The importance of this transporter was further supported by knockout mice that were not viable after birth. CAT-1 was the first amino acid transporter to be cloned; several other CATs were later characterized biochemically and molecularly. These transporters mediate the bidirectional transport of cationic amino acids, thus supporting important metabolic functions, such as synthesis of proteins, nitric oxide (NO) synthesis, polyamine biosynthesis, and interorgan amino acid flow. This review briefly describes the advances in the regulation of cationic amino acid transport, focusing on the molecular mechanisms that regulate the CAT-1 transporter. Of particular interest to this review is the regulation of CAT-1 by nutritional stresses, such as amino acid availability. The studies that are reviewed conclude that the CAT-1 gene is essential for cell survival during stress because it allows cells to resume growth as soon as amino acids become available.

Amino acid intake during lactation and amino acids of plasma and human milk

The aim of this study was to determine the free amino acid pool in plasma and milk in marginally nourished lactating women. Twenty-eight rural women (age, 23.9+/-5y; weight 50.2+/-4.9 kg; height, 148.2+/-4.8 cm) were studied under metabolic balance conditions. Subjects were divided into 6 groups (5-6 women in each), representing rural mothers postweaning and in the 15, 3rd, and 6th months of lactation; nonpregnant, nonlactating controls were from rural and urban areas. Amino acid analyses of diet and of plasma and milk samples were performed using a Beckman 6300 amino acid analyzer. Lysine intakes were lower than the recommended intake for lactating women (RDA). Plasma amino acid profiles differed between the lactating and weaned groups: aspartate and isoleucine increased at the 6th month (P < 0.05), while valine declined over weaning time (P < 0.05). In milk, valine and proline decreased at the 6th month (P < 0.05), while serine rose at the 3rd month. Free amino acid pools were 1- to 15-fold higher in plasma than in milk for branched-chain amino acids and basic, aromatic, and neutral amino acids. In mammary tissue these amino acids can be channeled to tissue and milk protein synthesis or to catabolic pathways. Glutamate was 40-fold higher in milk with respect to plasma content. This was the predominant amino acid in the free amino acid pool in milk. These results suggest selective amino acid transport in mammary tissue during lactation.

Peripheral and splanchnic metabolism of dietary nitrogen are differently affected by the protein source in humans as assessed by compartmental modeling

We used a previously developed compartmental model to assess the postprandial distribution and metabolism of dietary nitrogen (N) in the splanchnic and peripheral areas after the ingestion of a single mixed meal containing either (15)N-labeled milk or soy purified protein. Although the lower whole-body retention of dietary N from soy protein was measured experimentally, the splanchnic retention of dietary N was predicted by the model not to be affected by the protein source, and its incorporation into splanchnic proteins was predicted to reach approximately 35% of ingested N at 8 h after both meals. However, dietary N intestinal absorption and its appearance in splanchnic free amino acids were predicted to be more rapid from soy protein and were associated with a higher deamination, concomitant with a higher efficiency of incorporation of dietary N into proteins in the splanchnic bed. In contrast, soy protein was predicted to cause a reduction in peripheral dietary N uptake, as a consequence of both similar splanchnic retention and increased oxidation compared with milk protein. In addition, protein synthesis efficiency was reduced in the peripheral area after soy protein intake, leading to dietary N incorporation in peripheral proteins that fell from 26 to 19% of ingested N 8 h after milk and soy protein ingestion, respectively. Such a model thus enables a description of the processes involved in the differential metabolic utilization of dietary proteins and constitutes a valuable tool for further definition of the notion of protein quality during the period of protein gain.

Temporal response of hepatic threonine dehydrogenase in chickens to the initial consumption of a threonine-imbalanced diet

Amino acid imbalances contribute to higher requirements of amino acids than would occur if the dietary profile of amino acids perfectly matched the requirements. The mechanisms of imbalances have not been fully elucidated. Because threonine dehydrogenase (TDH) activity in liver mitochondria increases in chicks and rats subjected to threonine imbalance, the current study was carried out to determine whether the change in TDH activity occurs rapidly enough after the consumption of an imbalanced diet to be considered a possible primary metabolic response. In a series of experiments, Leghorn chicks were allowed free access to a semipurified basal diet marginally limited in threonine or the same diet containing a mixture of indispensable amino acids (IAA) lacking threonine to cause a threonine imbalance. In the first experiment, dietary supplements of 5.5 and 11.1% IAA were used to determine a level of supplement that would cause a robust response in the specific activity of TDH. Feed intake, body weight gains and efficiency of feed utilization were lower and specific activities of TDH were higher in chicks fed 11.1% IAA than in those fed 5.5% IAA. In subsequent experiments, hepatic TDH activities and plasma amino acid profiles of the control and experimental groups were determined at 1. 5, 3, 6, 12 and 24 h after the first offering of the diet containing 11.1% IAA. The specific activities of TDH in chicks fed the IAA supplement were 40-150% higher (P < 0.05) and plasma threonine concentrations were 42-53% lower (P < 0.05) than in chicks fed the basal diet at all times except 1.5 h. These results indicate that changes in the capacity for threonine degradation via TDH may occur in the liver within a few hours after the consumption of a threonine-imbalanced diet and suggest the possibility that altered TDH activity may contribute to the increased threonine requirement associated with threonine imbalance.

Endogenous liver carcinogenesis in the rat

Carcinogenesis may be effected not only through exposure to exogenous stimuli but also by genetic and epigenetic influences derived from endogenous factors. In the latter case, the mechanisms are still largely obscure because of the limited availability of appropriate in vivo experimental models. However, continuous feeding of a diet deficient in choline and methionine is well known to cause hepatocellular carcinomas (HCC) in rats in the absence of any known exogenous carcinogens and can serve as a good research model. A semi-synthetic, choline-deficient, L-amino acid-defined (CDAA) diet, containing practically no choline and low methionine, induces HCC with a background of fatty liver and hepatocyte death, subsequent regeneration and fibrosis resulting in cirrhosis. Using the CDAA diet, we have revealed the participation of oxidative injury to DNA and other subcellular components and of alteration in intrahepatic signal transduction pathways in the mechanisms underlying this rat liver carcinogenesis model. In the present paper, the current understanding of endogenous rat liver carcinogenesis, due to dietary choline deficiency, is reviewed.

Can amino acid requirements for nutritional maintenance in adult humans be approximated from the amino acid composition of body mixed proteins?

The quantitative needs for the dietary indispensable amino acids in adult human protein nutrition are still poorly established. Tracer studies with 13C-labeled amino acids have been undertaken previously in our laboratories to reevaluate and further determine the minimum physiological needs for selected indispensable amino acids in healthy adult volunteers. For those amino acids that have not yet been studied by this approach we have proposed a tentative set of requirement figures based on considerations of the amino acid composition of body mixed proteins and the rate of obligatory amino acid losses (i.e., losses when the diet contains no proteins or amino acids). Here we provide an argument for, and a justification of, this approach as an interim measure until more comprehensive data become available on the quantitative aspects of amino acid metabolism in healthy humans.

The distribution and turnover of 35S methionine as influenced by diet in the dark-eyed Junco (Junco hyemalis)

1. Dark-eyed Juncos (Junco hyemalis) were maintained on one of three semi-synthetic diets, differing only in their sulphur amino acid content. 2. 35S-methionine was administered intraperitoneally after 3 days on their respective diets and the animals were killed 24 or 96 hr post-injection. 3. Faecal loss of 35S-methionine was significantly lower in the low methionine/high cysteine (HC) group after 24 hr when compared with other two dietary groups (4.69 vs 5.53 and 5.47%) indicating a whole-body conservation of the limiting amino acid. 4. Incorporation of 35S-methionine in hepatic and intestinal tissues was also greater in the HC group, even as the animals were losing body weight.

Effect of type of protein on food intake of rats fed high protein diets

The effects of type of protein on intake of a high protein diet after adapting rats to a low protein diet were examined in rats trained to eat a 5.2% (N X 6.25) protein diet containing a mixture of casein, lactalbumin, egg white and soy protein, in a single 3-hour period per day. Food intake was measured from 0-15, 15-30, 30-90, and 90-180 minutes. After a 2-week adjustment period, rats were presented with a 40% (N X 6.25) protein purified diet containing only one of the 4 proteins mentioned above or a mixture of these 4 proteins. During the first 15-minute interval, rats eating diets containing protein mixture, lactalbumin, egg white or soy protein depressed their intake significantly compared with the average intake of the 3-day pre-test period, whereas rats eating casein diet increased their intake. During the last 90-minute interval of the first day, all rats depressed their intake, those rats eating casein the least and those rats eating egg white the most. On the second day, rats offered lactalbumin depressed their intake 52.5% for the 3-hour period and rats offered casein depressed their intake 34.3%. Rats eating soy protein, egg white and protein mixture increased their intake from day 1 to day 2. These experiments show that type of protein affects rats' initial intake when they are offered a high protein diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of totally synthetic, low phenylalanine diet on adolescent phenylketonuric patients

The long-term responses of 5 adolescent phenylketonuric patients to chemically-defined, synthetic diets with normal and low phenylalanine content were determined. The synthetic preparations were found capable of sustaining good health and rapid growth in this group of profoundly retarded, behaviourally disturbed patients over a 3½-year period without clinical or biochemical evidence of nutritional inadequacy. 4 of these patients who were treated for 6 months on a comparable diet, in which 80% of the phenylalanine was replaced by tyrosine, continued to show weight maintenance and height increases. There was no evidence of poor acceptability of the imbalanced diet, whether the blood phenylalanine concentrations were at phenylketonuric or treatment levels. The phenylalanine intake required to maintain blood phenylalanine concentrations of 3-5 mg/100 ml in these 4 patients was well below normal requirements, and ranged between 6·8 and 20·1 mg/kg per day. Predictably, the phenylalanine requirement varied with individual growth rates. All 4 treated patients had objective signs of improved central nervous system function during the six-month period on the phenylalanine-restricted diet. These electrophysiological and behavioural improvements were manifest after blood phenylalanine concentrations fell below 12 mg/100 ml in 3 cases and below 5 mg/100 ml in the fourth.