Excess dietary Lys reduces feed intake, stimulates jejunal CCK secretion and alters essential and non-essential blood AA profile in pigs.

BACKGROUND: Commercial diets are frequently formulated to meet or exceed nutrient levels including those of limiting essential amino acids (AA) covering potential individual variations within the herd. However, the provision of dietary excess of AA, such as Lys, may lead to reduced appetite and growth in pigs. The mechanisms modulating these responses have not been extensively investigated. This study evaluated the effect of Lys dietary excesses on performance and satiety biomarkers in post weaning pigs. METHODS: Twenty-four pigs aged 21 d and weighing 6.81 ± 0.12 kg (mean ± SEM) were individually housed and offered 1 of 4 dietary treatments for 3 weeks: a diet containing a standardized ileal digestible Lys reaching 100% (T0), 120% (T1), 150% (T2) or 200% (T3) of the NRC (2012) requirements. At the end of the experiment, blood samples from the cephalic vein of the T0 and T3 groups were obtained for AA analysis. In addition, primary intestinal cultures from T0 pigs were used, following their humane killing, to evaluate the effect of Lys on gut hormone secretion and AA sensors gene expression under ex vivo conditions. RESULTS: Feed intake was linearly reduced (P < 0.001) and the weight gain to feed ratio reduced (P < 0.10) with increased dietary levels of Lys during the third- and first-week post weaning, respectively. Cholecystokinin concentration (P < 0.05) and the metabotropic glutamate receptor 1 and the solute carrier family 7 member 2 (P < 0.10) gene expression was enhanced in proximal jejunum tissues incubated with Lys at 20 mmol/L when compared to the control (Lys 0 mmol/L). Plasma Lys and Glu (P < 0.05) concentration increased in the T3 compared to T0 pigs. In contrast, plasma levels of His, Val, Thr, Leu (P < 0.05) and Gln (P < 0.10) were lower in T3 than T0 pigs. CONCLUSION: The present results confirm that excess dietary Lys inhibits hunger in pigs. Moreover, the results provide evidence of pre- and post-absorptive mechanisms modulating these responses. Lys dietary excesses should be narrowed, when possible, to avoid negative effects of the AA on appetite in pigs.

Leucine (and lysine) increased plasma levels of the satiety hormone cholecystokinin (CCK), and phenylalanine of the incretin glucagon-like peptide 1 (GLP-1) after oral gavages in pigs.

Excess dietary amino acids (AA) has been associated with reduced feed intake, increased satiation, and extended satiety in pigs. Recent ex vivo studies suggested that satiety peptide cholecystokinin (CCK) and insulinotropic glucagon-like peptide 1 (GLP-1), mediated the anorexigenic or insulinotropic effects of Lys, Glu, Phe, Ile, and Leu. However, the ex vivo model limitations require validation in vivo. The aim of the present study was to assess the effect of orally administered AA in vivo in pigs. It was hypothesized that oral Lys, Ile, and Leu have an anorexigenic effect via CCK, while Glu and Phe have an insulinotropic effect increasing circulating levels of GLP-1. Eight entire male pigs (Landrace × Large White) of 18.23 ±â€…1.06 kg of body weight were administered an oral gavage of water (control) or a 3 mmol/kg of Glu, Ile, Leu, Lys, Phe, or glucose (positive control for GLP-1 release) following an overnight fasting during 5 consecutive days using an incomplete latin square design. Blood samples were collected from the jugular vein before (-5 min, baseline value) and after the gavage (5, 15, 30, 60 and 90 min) to assess CCK and GLP-1 plasma levels. Pigs administered the oral gavage of Leu (P < 0.05), or Lys (P < 0.1) had increased levels of plasma CCK from 0 to 90 min post-gavage when compared to the control. A strong association (P < 0.001) was observed between GLP-1 plasma levels with Phe intake. The impact was significant starting 30 min post-gavage and was sustained until the end of the experiment (90 min post-gavage). Glucose administration increased GLP-1 early after the intake at the 5 min mark (P < 0.1). A positive correlation (P < 0.05, r = 0.89) driven by the impact of Phe at the 60 to 90 min post-gavage was identified between CCK and GLP-1 indicating feedback mechanisms between proximal and distal small intestine. In conclusion, oral gavages of Leu and Lys increased anorexigenic hormone CCK plasma levels in pigs. Phe caused a significant long-lasting increase in incretin GLP-1 plasma levels. Blood CCK and GLP-1 concentrations in Phe gavaged pigs were positively correlated indicating a potential feedback mechanism between proximal (CCK) and distal (GLP-1) small intestine. The present results are compatible with the known anorexigenic effects of excess dietary Leu and Lys, and the insulinotropic effect of Phe in pigs. These results demonstrate the relevance of accurate feed formulation practices particularly in post weaning pigs.

Previous ex vivo studies showed how the amino acids (AA) Lys, Leu, Ile, Phe, and Glu increased satiety peptide cholecystokinin (CCK) and/or insulinotropic hormone glucagon-like peptide 1 (GLP-1) model in pigs. The objective of this study was to validate the ex vivo model by testing the AA of interest in live pigs. Following the oral administration by gavage Leu increased plasma CCK compared to water. Phe showed a sustained long-lasting increase in GLP-1 plasma levels appearing 30 min after the gavage. A positive correlation between CCK and GLP-1 blood levels was observed for Phe treated pigs between 60 and 90 min after the treatment indicating that GLP-1 may induce the release of CCK in the small intestine via feedback mechanisms. The results also showed a trend for Lys increasing CCK congruent with previous data reporting an inhibition of appetite by dietary excess of this AA. These findings are relevant for commercial feeding practices since Lys is often supplemented and dietary Leu is commonly high in pig feeds. Finally, our results highlight the relevance of aromatic AA (i.e., Phe), in pig nutrition that deserves additional attention. There is significant room for improving the understanding of optimal AA levels in pig feeds.

An oral gavage of lysine elicited early satiation while gavages of lysine, leucine, or isoleucine prolonged satiety in pigs.

Excess dietary amino acids (AA) may negatively affect feed intake in pigs. Previous results showed that Lys, Leu, Ile, Phe, and Glu significantly increased gut peptide secretion (i.e., cholecystokinin, glucagon-like peptide 1). However, the link between dietary AA and gut peptide secretion with changes in feeding behavior patterns has not been demonstrated to date in pigs. The aim of the present study was to determine the effect of Lys, Leu, Ile, Phe, and Glu, on feed intake and meal patterns in young pigs. Twelve male pigs (Landrace × Large White, body weight = 16.10 ± 2.69 kg) were administered an oral gavage of water (control) or Lys, Leu, Ile, Phe, Glu, or glucose (positive control) at 3 mmol.kg-1 following an overnight fasting. The experiment consisted in measuring individual feed disappearance and changes in meal pattern (including latency to first meal, first meal duration, intermeal interval, second meal duration, and number of meals) based on video footage. Compared to the control group Lys significantly (P ≤ 0.01) reduced feed intake during the first 30 min and up to 2.5 h post-gavage, including a reduction (P ≤ 0.05) in the first meal duration. Similarly, Leu and Ile also significantly decreased feed intake up to 3 h post-gavage on a cumulative count. However, the strongest (P ≤ 0.01) impacts on feed intake by the two branched chained AA were observed after the first- or second-hour post-gavage for Leu or Ile, respectively. In addition, Leu or Ile did not affect the first meal duration (P ≥ 0.05). Leu significantly increased (P ≤ 0.01) the intermeal interval while decreasing (P ≤ 0.05) the number of meals during the initial 2 h following the gavage when compared with the control group. In contrast, the oral gavages of Phe or Glu had no significant impact (P > 0.05) on the feeding behavior parameters measured relative to the control pigs. In turn, glucose had a short-lived effect on appetite by reducing (P < 0.05) feed intake for 30 min after the first-hour post-gavage. In conclusion, the impact of an oral gavage of Lys on feeding behavior is compatible with a stimulation of early satiation and an increased duration of satiety. The main impact of the oral gavages of Leu and Ile was an increase in the duration of satiety. The gastrointestinal mechanisms associated with non-bound dietary AA sensing and the impact on voluntary feed intake warrant further investigations.

A better understanding of the impact of individual dietary amino acids on feeding behavior in pigs can help improve current feed formulation practices. Lys, Leu, Ile, Phe, or Glu were selected based on the impact on gut peptide secretion from a previous study, to assess the effect on feed intake and meal pattern using an oral gavage model (3 mmol.kg−1) in young pigs. The oral gavage of Lys resulted in early satiation as indicated by the reduction of the first meal duration and the feed intake within the first 30 min post-gavage. In addition, the Lys group showed reduced feed intake up to 3 h post-gavage, interpreted as an extended duration of the post first meal satiety compared to the control. The latter was also observed for the branched chained amino acids (BCAA) Leu and Ile. The Leu gavage resulted in an increased intermeal interval together with a reduction on the number of meals while Ile, in turn, reduced feed intake particularly during the third hour post-gavage. No significant effects of the Phe or Glu gavages on feeding behaviors were observed. Overall, these results suggest that dietary Lys, Leu, or Ile had significant anorexigenic effects. Lys increased both satiation and satiety while the BCAA Leu and Ile, mainly increased post-meal satiety in pigs.

CCK and GLP-1 release in response to proteinogenic amino acids using a small intestine ex vivo model in pigs.

The impact of individual amino acids (AA) on gut hormone secretion and appetite regulation in pigs remains largely unknown. The aim of the present study was to determine the effect of the 20 proteinogenic AA on the release of the anorexigenic hormones cholecystokinin (CCK) and glucagon-like peptide 1 (GLP-1) in postweaning pigs. Six 25-d-old male piglets (Domestic Landrace × Large White; body weight = 6.94 ± 0.29 kg) were humanely killed for the collection of intestinal segments from the duodenum, jejunum, and ileum. Tissue samples from the three intestinal segments were used to determine which of the regions were more relevant for the analysis of gut peptides. Only the segments with the highest CCK and GLP-1 secretion and expression levels were evaluated with the 20 individual AA. Tissue segments were cut open, cleaned, and stripped of their muscle layer before identical circular samples were collected and incubated in 24-well plates for 1 h (37 °C, 5% v/v CO2). The culture broth consisted of a glucose-free KRB buffer containing no added AA (control) or with the addition of 10 mM of 1 of the 20 proteinogenic AA. Following incubation, tissues and supernatant were collected for gene expression and secretion analysis of CCK and GLP-1 levels. CCK secretion and mRNA expression were higher (P < 0.05) in duodenum when compared with proximal jejunum or ileum, whereas GLP-1/proglucagon levels were higher in ileum vs. duodenum (P < 0.05) and jejunum (P < 0.05, for GLP-1 only) in postweaning pigs. Based on these results, the effect of AA on CCK and GLP-1 secretion was studied in the duodenum and ileum, respectively. None of the AA tested stimulated both anorexigenic hormones. Of all the essential AA, Ile, Leu, Met, and Trp significantly (P < 0.05) stimulated GLP-1 from the ileum, while only Phe stimulated CCK from the duodenum. Of the nonessential AA, amide AA (Gln and Asn) caused the release of CCK, while Glu and Arg increased the release of GLP-1 from the ileum. Interpreting the results in the context of the digestion and absorption dynamics, non-bound AA are quickly absorbed and have their effect on gut peptide secretion limited to the proximal small intestine (i.e., duodenum), thus, mainly CCK. In contrast, protein-bound AA would only stimulate CCK release from the duodenum through feedback mechanisms (such as through GLP-1 secreted mainly in the ileum).

Understanding which dietary amino acids (AA) may impact the release of gut hormones involved in the modulation of feed intake, such as cholecystokinin (CCK) and glucagon-like peptide 1 (GLP-1), can help improve pig feed formulations. The series of studies presented assessed the effect of the 20 proteinogenic non-bound AA on the secretion of CCK and/or GLP-1 by duodenum, jejunum, and/or ileum samples from postweaning piglets. None of the AA tested stimulated the secretion of both CCK and GLP-1. Among the essential AA (EAA), Ile, Leu, Met, and Trp significantly stimulated GLP-1 from the ileum, while Phe stimulated CCK from the duodenum. Of the non-essential AA (NEAA), AA amides Gln and Asn caused the release of CCK, while Glu and Arg increased the release of GLP-1 from the ileum. The results suggest that both non-bound EAA and NEAA participate in appetite control via the release of gut peptides in pigs. Given that CCK was mainly released from duodenum samples (in the pre-enzymatic section of the small intestine), protein-bound AA could only influence CCK release through feedback mechanisms such as through the presence of GLP-1 receptors.

Cinnamaldehyde Induces Release of Cholecystokinin and Glucagon-Like Peptide 1 by Interacting with Transient Receptor Potential Ankyrin 1 in a Porcine Ex-Vivo Intestinal Segment Model.

Cinnamaldehyde and capsaicin have been reported to exert effects on the gastric function, mediated by the interaction with transient receptor potential ankyrin channel 1 (TRPA1) and transient receptor potential vanilloid channel 1 (TRPV1), respectively. This study examined whether these compounds could trigger the release of cholecystokinin (CCK) and/or glucagon-like peptide 1 (GLP-1) in the pig's gut in a porcine ex-vivo intestinal segment model. Furthermore, it was verified whether this response was mediated by TRPA1 or TRPV1 by using the channel's antagonist. These gut peptides play a key role in the "intestinal brake", a feedback mechanism that influences the function of proximal parts of the gut. Structural analogues of cinnamaldehyde were screened as well, to explore structure-dependent activation. Results showed a significant effect of capsaicin on GLP-1 release in the proximal small intestine, TRPV1 independent. TRPA1 showed to be strongly activated by cinnamaldehyde, both in proximal and distal small intestine, evidenced by the release of CCK and GLP-1, respectively. Out of all structural derivates, cinnamaldehyde showed the highest affinity for TRPA1, which elucidates the importance of the α,ß-unsaturated aldehyde moiety. In conclusion, cinnamaldehyde as a TRPA1 agonist, is a promising candidate to modulate gastric function, by activating intestinal brake mechanisms.

Socially conditioned flavor preferences with fluids: Transfer with solid foods, palatability, and testing constraints.

In two experiments, the social influence on choosing between two novel diets was analyzed. In Experiment 1, a group of rats (demonstrators) ingested a novel flavor cue presented in powdered food or in a 4% sucrose solution. Afterwards, demonstrators interacted with a group of observer rats for 30 minutes. Preferences for the cue flavor and another flavor were tested in observers using a two-choice test in the same or in the opposite substrate (solid/liquid) as their demonstrators. When tested with solid foods, observers displayed higher intake of the flavor consumed by the demonstrators, regardless of whether the demonstrators had consumed it as a solid or liquid. However, when observers were tested with solutions, there was no demonstration of the same preference. Experiment 2 focused on solutions, presenting them at test either with the flavor as a water solution alone, or as a solution plus an aerosol presentation. In addition, a single-cue testing procedure was used to allow examination of the palatability (assessed through the analysis of licking behavior) of the test solutions. Under single-cue testing procedures with solutions, observer rats did consume more of the flavors previously consumed by the demonstrator animals, but there was no effect of social learning on the palatability of the test flavors. These results suggest that socially conditioned flavor preferences can be reliably observed with fluid solutions, will transfer between different substrates, and affect consumption to a greater degree than palatability. However, future experiments need to be performed to confirm some of these suggestions.