Dietary l-Tryptophan Supplementation Enhances the Intestinal Mucosal Barrier Function in Weaned Piglets: Implication of Tryptophan-Metabolizing Microbiota

Abstract

l-Tryptophan (Trp) is known to play an important role in the health of the large intestine. However, a role of dietary Trp in the small-intestinal mucosal barrier and microbiota remains poorly understood. The present study was conducted with weaned piglets to address this issue. Postweaning piglets were fed for 4 weeks a corn- and soybean meal-based diet supplemented with 0 (Control), 0.1, 0.2, or 0.4% Trp. The small-intestinal microbiota and serum amino acids were analyzed by bacterial 16S rRNA gene-based high-throughput sequencing methods and high-performance liquid chromatography, respectively. The mRNA levels for genes involved in host defense and the abundances of tight-junction proteins in jejunum and duodenum were measured by real time-PCR and Western blot techniques, respectively. The concentrations of Trp in the serum of Trp-supplemented piglets increased in a dose-dependent manner. Compared with the control group, dietary supplementation with 0.2–0.4% Trp reduced the abundances of Clostridium sensu stricto and Streptococcus in the jejunum, increased the abundances of Lactobacillus and Clostridium XI (two species of bacteria that can metabolize Trp) in the jejunum, and augmented the concentrations of secretory immunoglobulin A (sIgA) as well as mRNA levels for porcine β-defensins 2 and 3 in jejunal tissues. Moreover, dietary Trp supplementation activated the mammalian target of rapamycin signaling and increased the abundances of tight-junction proteins (zonula occludens (ZO)-1, ZO-3, and claudin-1) in jejunum and duodenum. We suggested that Trp-metabolizing bacteria in the small intestine of weaned pigs primarily mediated the beneficial effects of dietary Trp on its mucosal integrity, health, and function.

Maternal Tryptophan Supplementation Protects Adult Rat Offspring against Hypertension Programmed by Maternal Chronic Kidney Disease: Implication of Tryptophan-Metabolizing Microbiome and Aryl Hydrocarbon Receptor

“…Several bacterial species have been reported to produce tryptophan metabolites [ 5 , 30 , 31 ], such as Lactobacillus, Bacteroides, Bifidobacterium, Peptostreptococcus , Ruminococcus, Ruminiclostridium, and Clostridium. Although tryptophan supplementation in pregnancy shaped a different microbiome profile compared to the controls, most tryptophan-metabolizing microbes were not altered.…”

L-Tryptophan Enhances Intestinal Integrity in Diquat-Challenged Piglets Associated with Improvement of Redox Status and Mitochondrial Function

“…Moreover, weaning stress-induced intestinal barrier dysfunction, characterized by increased intestinal permeability, has been shown to be one of the primary causes of severe diarrhea and reduced growth performance of post-weaning piglets [3]. Tryptophan (Trp) is the second-limiting amino acid in most corn-based diets of pigs, and functionally regulates body protein synthesis and improves stress and immune responses [4,5]. Several studies have shown that dietary supplementation with Trp enhances intestinal integrity and reduces diarrhea rate, thereby improving growth performance [6,7].…”

“…Interestingly, the authors from the same group, which concluded that a Trp-supplemented diet impaired the intestinal integrity of piglets, contended that a 0.15% Trp-supplemented diet increased villus height to crypt depth ratio without affecting intestinal permeability [9]. A more recent study stated that weaning piglets fed the 0.20% or 0.4% Trp-supplemented diet exhibited enhanced intestinal mucosal barrier function than those fed the basal diet [5]. Therefore, it can be concluded that a proper dosage of Trp supplemented in the diet would be favorable for the enhancement of intestinal integrity and the improvement of growth performance of nursery piglets.…”

Nutritional Therapy to Modulate Tryptophan Metabolism and Aryl Hydrocarbon-Receptor Signaling Activation in Human Diseases

“…Not only did additional (L-)tryptophan (L-Trp) lead to restoration of AhR ligand production by the gut microbiota, it also increased AhR mRNA expression, decreased the expression of the pro-inflammatory cytokines and upregulated of the anti-inflammatory cytokine IL-22 production in mice and porcine DSS models [ 136 , 137 ]. Additional L-tryptophan in weanling piglets also enhanced intestinal mucosal barrier function by improving tight junctions [ 138 ].…”