The gut microbiota plays a crucial role in regulating host amino acid availability and metabolism through complex interactions with the host metabolic processes. This review summarizes three main mechanisms through which the microbiota influences host amino acid homeostasis. Firstly, gut microbiota actively competes for luminal amino acids derived from the diet and concurrently contributes to the host's amino acid pool through de novo biosynthesis. Secondly, they modulate host intestinal hydrolases and amino acid transporters, thereby fine-tuning amino acid absorption and systemic bioavailability. Thirdly, microbially secreted factors, including diverse metabolites and extracellular vesicles, reprogram host amino acid metabolic pathways. The inherent inter-individual variations in microbial composition and metabolic capacity highlight the necessity of personalized therapeutic strategies targeting the microbiota. By summarizing current findings, this review aims to provide a deeper understanding of this dynamic interplay and to identify promising avenues for future investigations in the field.

Obesity is a nutritional disorder caused by an imbalance between energy intake and expenditure. The natural products will provide hypolipidemic active factors that will intervene in obesity and its complications, as well as direct drug treatment. Artemisia argyi leaf is a well-known species in traditional Chinese medicine, and its essential oil (AAEO) has been identified to exert various physiological activities. This study investigates the chemical composition of essential oil extracted from Artemisia argyi (AAEO) and its potential effects on intestinal microbial function and lipid metabolism in mice subjected to a high-fat diet (HFD). The essential oil was extracted and analyzed for its bioactive compounds, revealing a rich presence of terpenes and oxygenated derivatives. Utilizing LC-MS/MS technology combined with multivariate statistical methods, significant alterations in serum metabolites were observed in AAEO-treated mice compared to those on HFD alone. Key metabolic pathways impacted by AAEO included linoleic acid metabolism and glycerophospholipid metabolism. These findings suggest that while AAEO did not significantly alter gut microbiota composition, it substantially modulated lipid metabolism via linoleic acid and glycerophospholipid pathways, suggesting a potential natural strategy for obesity-related metabolic disorders. This study provides new insights into the application of Artemisia argyi essential oil in dietary interventions and obesity management.

Background: The early nutritional metabolism of piglets is intimately associated with the regulation of immune function, and amino acids play a crucial role in modulating the fate and function of porcine immune cells, especially macrophages. However, the metabolic changes upon macrophage activation remain elusive. Methods: We established an in vitro activation model of porcine macrophages and investigated alterations in metabolites involved in polyamine and tryptophan metabolism upon activation by various toll-like receptor (TLR) activators. Results: TLR activation inhibits the production of spermine and alters the kynurenine pathway of the tryptophan metabolism toward the kynurenic acid biosynthesis. Specifically, TLR9 activation redirects the metabolic pathway of tryptophan toward kynurenic acid synthesis, which subsequently inhibits melatonin production via the protein kinase A (PKA)/cyclic adenosine monophosphate (cAMP)/cAMP-responsive element-binding protein (CREB) signaling pathways. Conclusions: TLR activation reprograms the polyamine and tryptophan metabolism in porcine macrophages. Knowledge of the metabolic alterations in polyamine and tryptophan upon TLR activation in macrophages offers valuable insights and potential strategies for nutritional intervention to enhance piglet immunity.

Weaning stress frequently compromises intestinal integrity and nutrient absorption in piglets and induces structural perturbations in the gut microbiota. This study investigated the effects of dietary Paramylon, a linear β-1,3-glucan from Euglena gracilis, on growth and intestinal function. A total of 32 healthy, 21-day-old weaned piglets (male, castrated, Duroc × Landrace × Yorkshire) were randomly allocated to four groups: control, 0.025%, 0.05%, and 0.1% Paramylon (8 pigs/group). The results showed that 0.05% dietary Paramylon quadratically increased average daily gain and feed intake (p < 0.05). Serum TC content significantly increased, while the serum urea level significantly decreased (p < 0.05). This optimal dose was used for mechanistic exploration. Dietary 0.05% Paramylon notably enhanced ileal morphology, increasing the villus height to crypt depth ratio (p < 0.01) and significantly improving apparent nutrient digestibility and ileal β-amylase activity (p < 0.05). The expression levels of SLC7A1 and GLUT2 in ileum tissues were significantly upregulated (p < 0.05). The expression level of SLC7A7 in the liver was also increased (p < 0.05). This nutrient transport-promoting effect was further confirmed in IPEC-J2 cells, which manifested because 10 ng/mL of pure Paramylon significantly upregulated the gene expressions of SLC38A2, EAAT3, PEPT1, and GLUT2 (p < 0.05). KEGG enrichment analysis on the ileum indicated that differentially abundant metabolites were enriched in amino acid-related metabolic pathways. Furthermore, the 16s sequencing results revealed that Romboutsia was significantly enriched in the Paramylon group. In conclusion, Paramylon, as an effective dietary supplement, helps promote nutrient digestion and absorption in weaned piglets and contributes to maintaining intestinal health.