Table A1.
An overview of the research during the last two decades concerning the effects of dietary amino acids on gut health and functions in weanling pigs 1.
| Amino Acid(s) | Dietary Concentrations 2 |
Major Effects on the Gut Health Parameters Observed | Reference |
|---|---|---|---|
| Arginine | 0.6 vs. 0.0% | Increased the small intestinal growth, the villus height (VH), the crypt depth (CD), and the goblet cell counts in the mucosa | Wu et al. [31] |
| Arginine | 1.0 vs. 0.0% | Increased the epithelial VH and the mucosal vascular endothelial growth factor level of the small intestine; Reduced the CD in the duodenum and jejunum | Yao et al. [119] |
| Arginine | 1.0, 0.5, vs. 0.0% | Protecting and enhancing intestinal mucosal immune barrier function, and maintaining intestinal integrity after E. coli lipopolysaccharide (LPS) challenge | Zhu et al. [120] |
| Arginine | 0.8, 0.4, vs. 0.0% | Increased (linearly and quadratically) the VH, villus area, and CD; Increased (linearly and quadratically) the mucosal protein content | Yang et al. [32] |
| Arginine | 1.6, 0.8, vs. 0.0% | Decreased the CD and suppressed the inflammatory cytokine expression in the jejunum | Zheng et al. [121] |
| Glutamine | 2.0 vs. 0.0% | Mitigated villus atrophy and morphology disruption of the gut after Escherichia coli challenge | Yi et al. [20] |
| Glutamine | 0.5 vs. 0.0% | increased both VH and CD, decreased the VH to CD ratio (VCR); Increased in mitotic mucosal cells (M), decreased in apoptotic mucosal cells (A), thus decreasing the A:M index; The percentages of mucosal macrophages were greater | Domeneghini et al. [25] |
| Glutamine | 0.5 vs. 0.0% | Increased the VH and CD and decreased the VCR; Gut barrier function may be improved | Domeneghini et al. [16] |
| Glutamine | 4.4 vs. 0.0% | Reducing the mucosal cytokine response; Improving the intestinal barrier function | Ewaschuk et al. [122] |
| Glycyl-glutamine | 0.15 vs. 0.00% | Mediated the adverse effects of E. coli LPS on gut integrity; the proinflammatory response may be limited | Jiang et al. [21] |
| Alanyl-glutamine | 0.45, 0.30, 0.15, vs. 0.00% | Increased the VH and VCR in duodenum and jejunum; the digestive-absorption function may be enhanced via those digestive enzymes and nutrient transporters analyzed | Zou et al. [22] |
| Glutamate | 1.0 vs. 0.0% | Increased the VH and mucosal thickness in the jejunum; Having favorable effects on gut epithelium cell proliferation | Wu et al. [123] |
| Glutamate | 2.0 vs. 0.0% | Improved the intestinal integrity; influenced the expression of amino acid receptors and transporters in the jejunal mucosa | Lin et al. [24] |
| Glutamate | 2.0 vs. 0.0% | Alleviated the diquat-induced oxidative stress via enhancing the superoxide dismutase, total antioxidant capacity, and nitric oxide levels and inhibiting lipid oxidation subsequent with malondialdeyhde generation. | Yin et al. [88] |
| Monosodium glutamate | 4.0, 2.0, 1.0, 0.5, vs. 0.0% | Increased jejunal VH, DNA content, and antioxidative capacity; reduced the incidence of diarrhea | Rezaei et al. [23] |
| Glutamine + Glutmate | (1.0 + 0.0), (0.9 + 0.1), (0.8 + 0.2), vs. (0.0 + 0.0) | The combinational effects of glutamine and glutamate could not achieve that of glutamine alone | He et al. [18] |
| Glutamine; AminoGut 3 | 1.00; (0.88 to 0.66), vs. 0.00; 0.00% | Increased the jejunal VH by glutamine; increased the jejunal CD by AminoGut (glutamine + glutamate) | Cabrera et al. [19] |
| Methionine | 0.12 vs. 0.00% | Increased the VH in jejunum, decreased the CD in duodenum, and increased the VCR in all three sections; Increased the abundance of occludin and decreased the abundance of active caspase-3 in the jejunum | Chen et al. [34] |
| Methionine | 0.12 vs. 0.00% | Improved intestinal integrity and oxidative status | Su et al. [124] |
| Methionine | 0.145 vs. 0.000% | Enhanced the duodenum morphology in association with reducing oxidative stress; Improved glutathione production in the mucosa cells | Shen et al. [36] |
| Methionine hydroxy analogue-free acid | 0.10, 0.05, vs. 0.00% | Tended to decrease pH in the stomach, duodenum, jejunum, colon and rectum; The 0.10% group increased the VH in duodenum, jejunum and ileum, and the VCR in jejunum and ileum | Kaewtapee et al. [35] |
| Cysteine | 0.61 vs. 0.00% | Increased the synthesis of mucosal epithelial proteins, such as glutathione and mucin | Bauchart-Thevret et al. [37] |
| N-acetyl cysteine | 500 vs. 0 mg/kg | Possessing a constructive regulation on the changes of gut redox status and microbiota in response to weaning stress | Xu et al. [125] |
| Taurine | 0.1 vs. 0.0% | Decreased the stimulation of immune response to lipopolysaccharide; Improved intestinal epithelial barrier function | Tang et al. [126] |
| Sulfur amino acids 4 | 0.96, 0.85, 0.74, 0.63, vs. 0.53% | Improved intestinal digestive and absorptive functions via affecting the mucosal antioxidant systems in a dose-dependent manner | Zong et al. [33] |
| Tryptophan | 0.5 vs. 0.0% | Increased the VH and VCR but unaffected transport of macro molecules (indicating the gut permeability) | Koopmans et al. [45] |
| Tryptophan | 0.4, 0.2, vs. 0.0% | Altered intestinal microbial composition and diversity; Improved intestinal mucosal barrier function | Liang et al. [58] |
| Tryptophan | 0.75, 0.15, vs. 0.00% | Negatively affected intestinal morphology (increased CD, decreased VCR) and decreased the mRNA expression of some tight junction proteins | Tossou et al. [127] |
| Threonine | 3.2, 2.2, 1.2, 0.5, vs. 0.0 g/kg | Increased the humoral antibody production and serum specific IgG concentrations | Wang et al. [128] |
| Threonine | 11.1, 7.5, vs. 3.7 g/kg | Improved the intestinal morphology and mucosa immune function; had beneficial effects in maintaining jejunal morphology integrity and repairing villous damage caused by E. coli challenge | Ren et al. [42] |
| Threonine | 0.2 vs. 0.0% | Improved the intestinal mucin synthesis and immune function; attenuated ileal inflammatory responses, of the intrauterine growth-retarded weanling piglets | Zhang et al. [71] |
| Threonine | 0.12 vs. 0.00% | Seemed to have greater benefits with a simple diet (contained soybean meal as a protein source) than with a complex diet (contained animal protein sources) in intestinal morphology, production of gut microbial metabolites, and inflammatory status in the jejunum | Koo et al. [43] |
| Branched-chain amino acids 5 | Leu (1.38 vs. 1.26%), Ile (0.80 vs. 0.60%), Val (1.01 vs. 0.74%) | Enhanced intestinal development (increased VH or reduced CD), and intestinal expression of several amino acid and peptide transporters | Zhang et al. [129] |
| Aspartate | 1.0, 0.5, vs. 0.0% | Attenuated LPS-induced intestinal damage indicated by greater VH and VCR as well as higher RNA/DNA and protein/DNA ratios; Improved intestinal function indicated by increased mucosal disaccharidase activities; Improved intestinal energy status indicated by increased ATP, ADP and total adenine nucleotide contents, adenylate energy charge and decreased AMP/ATP ratio | Pi et al. [9] |
| Lysine 6 | 1.60, 1.23, vs. 0.86% | Lysine restriction inhibited intestinal lysine transport, and enhanced the richness and evenness of the microbiota composition and diversity | Yin et al. [57] |
| Amino acid blend (AAB) 7 | 1.00% AAB vs. 0.99% alanine | Improved the intestinal morphology, barrier function, and antioxidative capacity; Reduced the diarrhea incidence; Enhanced the intestinal expression of the heat shock protein-70 gene | Yi et al. [130] |
1 The terms of weaning pigs, weanling pigs, weaned pigs, weaner pigs, postweaning pigs, nursery pigs, and young piglets after weaning used by different researchers for this topic of study are all classified subjectively as weanling pigs in this table. 2 Unless specified, each value indicates a supplemental concentration on the top of the basal diet which already met the dietary requirement for the said amino acid. The last concentration on the list for each study is, in nearly all the studies, for the basal diet (a control group). 3 AminoGut (Ajinomoto do Brazil, São Paulo, Brazil) contained 10% glutamine and 10% glutamate. 4 Sulfur amino acids (SAA) contain methionine and cysteine. These concentrations (calculated) corresponded to 130, 115, 100, 85, and 70%, respectively, of the SAA:Lysine ratio that had been recommended by NRC [27]. 5 Branched-chain amino acids, including leucine (Leu), isoleucine (Ile) and valine (Val), were added to a low protein (17.9%) diet to meet the recommendations. The concentrations of other essential amino acids were at the same levels between the two diets. 6 The lysine concentrations (calculated) corresponded to 130, 100 and 70%, respectively, of the dietary lysine requirement recommended by NRC [26] or [27]. 7 The AAB included glutamate:glutamine:glycine:arginine:N-acetylcysteine at a ratio of 5:2:2:1:0.5 on a weight basis.