Optimized proteolytic resistance motif (DabW)-based U1-2WD: A membrane-induced self-aggregating peptide to trigger bacterial agglutination and death

Dendritic Antifungal Peptides as Potent Agents against Drug-Resistant Candida albicans and Biofilm

Candida albicans infection is a major public health problem, exacerbated by the emergence of drug-resistant fungi with the widespread use of antifungal drugs. Therefore, the development of novel antifungal drugs for drug-resistant C. albicans infections is crucial. We constructed a series of dendritic antifungal peptides (AFPs) with different chain lengths of fatty acids as hydrophobic ends and 2 or 3 protease-stable repeats (Arg-Pro) as dendritic peptide branches. Among them, C4-3RP exhibited excellent antidrug-resistant fungal and biofilm activity (GMall = 5.04 μM) and was nontoxic. Furthermore, C4-3RP demonstrated high protease stability and salt ion tolerance, making it highly effective in murine skin infection mediated by C. albicans. In addition, C4-3RP uses multiple mechanisms of action to achieve excellent antifungal effects. In conclusion, the construction of dendritic peptides holds substantial potential in the treatment of fungal infections and provides a broader perspective on the design of peptide-based antifungal drugs.

Combating Antibiotic-Resistant Bacterial Infection Using Coassembled Dimeric Antimicrobial Peptide-Based Nanofibers

The emergence of multidrug-resistant (MDR) pathogens, coupled with the limited effectiveness of existing antibiotics in eradicating biofilms, presents a significant threat to global health care. This critical situation underscores the urgent need for the discovery and development of antimicrobial agents. Recently, peptide-derived antimicrobial nanomaterials have shown promise in combating such infections. Amino acid noncovalent forces, notably π-π stacking and electrostatic interactions, remain underutilized for guiding the coassembly of peptides into bacteriostatic nanomaterials. Thus, we constructed a dimeric nanopeptide system using the disulfide bonds of cysteine. The self-assembly of dimeric peptides into nanofibers was realized by the interaction of π-π aromatic amino acids (Trp, Phe, and Pyr) and the electrostatic attraction between oppositely charged amino acids (Asp and Arg). The optimal dimeric peptide 2D2W exhibits potent antibacterial activity against resistant bacteria and is nontoxic. Mechanistically, 2D2W penetrated the outer membrane after electrostatic adsorption, resulting in plasma membrane depolarization, homeostatic disruption, and ultimately bacterial death. In a mouse model of peritonitis, 2D2W demonstrated efficacy in the in vivo treatment of bacterial infections. In conclusion, the design of dimeric nanopeptides co-driven by intermolecular forces provides a promising avenue for the development of high-performance antimicrobial nanomaterials. These advances may also facilitate the application and advancement of peptide-based bacteriostatic agents in clinical practice.

Positive Charge-Concentrated Dimeric Lipopeptides with Enhanced Protease Resistance: A Potential Solution for Systemic Bacterial Infections

Antimicrobial peptides (AMPs) show potential as antibiotic alternatives for bacterial infections; nevertheless, the susceptibility to proteases limits their broader utilization. This study developed engineered lipopeptides using antienzymolysis modifications and cysteine (Cys)-dimerization strategy. As the key parameters for the functioning of AMPs, hydrophobicity and positive charges were concentrated within the peptide sequence by adjusting the intermolecular disulfide bond placement to study their distribution effects. Their centralization in the sequence induces a differential propensity of engineered lipopeptides toward bacterial membranes. Positive charge-concentrated dimeric lipopeptide (C-C10)C-C displayed strong resistance to various proteases, and demonstrated excellent stability and activity in vitro, effectively eliminating systemic bacterial infections in mice without eliciting in vivo toxicity. The bactericidal effects of (C-C10)C-C were achieved through a synergistic mechanism involving membrane cleavage and the inhibition of energy metabolism. In summary, these advances offered valuable insights into enhancing the protease resistance of AMPs and the potential for modifying peptide-based biomaterials through Cys-dimerization.

Cuminaldehyde Potentiates Antiproteolytic Peptide Efficacy via Parallel Pathways of Enhanced Inner Membrane-Damaging Activity and Inhibition of Bacterial Energy Metabolism

Antimicrobial peptides (AMPs) offer potential as antibiotic alternatives, but high cost, off-site cytotoxicity, and poor stability limit their application. Combining AMPs with adjuvants holds promise in surmounting these limitations. Among potentiators, terpenoids account for the highest proportion, yet their potential to enhance the AMPs efficacy and underlying mechanism remain unclear. Hence, we investigated the potential of monoterpenoids to enhance the efficacy of antiproteolytic AMPs N1 (NalAArIILrWrFR). Cuminaldehyde potentiated N1 activity against all tested strains, with FICI from 0.375 to 0.094. N1/cuminaldehyde combination also worked synergistically against drug-resistant bacteria, exhibited a low incidence of resistance development, and was not synergistically toxic to eukaryotes. Furthermore, cuminaldehyde enhanced N1 stability in salts, serum, and proteases. Mechanistically, cuminaldehyde enhanced the inner-membrane-damaging activity of N1 and inhibited bacterial energy metabolism. Finally, cuminaldehyde enhanced the efficacy of N1 against ETEC K88-induced enteritis in mice. Collectively, cuminaldehyde may be a promising N1 adjuvant to combat bacterial infections and circumvent antibiotic resistance.

Optimizing therapeutic efficacy of antifungal peptides via strategic terminal amino acid modification

INTRODUCTION

Antifungal peptides (AFPs) have the potential to treat antifungal-resistant infections; however, their structure-function relationship remains unknown, hindering their rapid development. Therefore, it is imperative to investigate and clarify the structure-function relationships of AFPs.

OBJECTIVES

This study aimed to investigate the impact of end-tagging single hydrophobic amino acids and capping the N-terminus with glycine (Gly) on the antifungal activity of peptide W4.

METHODS

The antifungal efficacy of the engineered peptides was initially assessed by determining the minimum inhibitory concentration (MIC) /minimal fungicidal concentration (MFC), killing kinetics, and drug resistance induction, in addition to evaluating the biocompatibility and stability. Subsequently, the antifungal mechanism was investigated using fluorescence labeling, electron microscopy, reactive oxygen species (ROS) detection, and measurement of mitochondrial membrane potential and apoptosis. The impact of the engineered peptides on Candida albicans (C. albicans) biofilm and their potential application in the scratch keratomycosis model were investigated.

RESULTS

The antifungal activity of W4 was significantly enhanced by capping Gly at the N-terminus, resulting in a decrease in average activity from 11.86 μM to 6.25 μM (GW4) and an increase in TI values by 1.9-fold (TIGW4 = 40.99). Mechanistically, GW4 exerted its antifungal effect by disrupting the cellular membrane structure in C. albicans, forming pores and subsequent leakage of intracellular contents. Concurrently, it facilitated intracellular ROS accumulation while decreasing the mitochondrial membrane potential. Additionally, GW4 demonstrated an excellent ability to inhibit and eliminate biofilms of C. albicans. Notably, GW4 demonstrated significant therapeutic potential in a C. albicans-associated keratitis model.

CONCLUSION

Capping Gly at the N-terminus increased residue length while significantly enhancing the helical propensity of W4, thereby augmenting its antifungal activity. Our exploratory study demonstrated the potential strategies and avenues for optimizing the structure-function relationships of AFPs and developing highly effective antifungal drugs.

Biomimetic Peptide Nanonets: Exploiting Bacterial Entrapment and Macrophage Rerousing for Combatting Infections

The alarming rise in global antimicrobial resistance underscores the urgent need for effective antibacterial drugs. Drawing inspiration from the bacterial-entrapment mechanism of human defensin 6, we have fabricated biomimetic peptide nanonets composed of multiple functional fragments for bacterial eradication. These biomimetic peptide nanonets are designed to address antimicrobial resistance challenges through a dual-approach strategy. First, the resulting nanofibrous networks trap bacteria and subsequently kill them by loosening the membrane structure, dissipating proton motive force, and causing multiple metabolic perturbations. Second, these trapped bacterial clusters reactivate macrophages to scavenge bacteria through enhanced chemotaxis and phagocytosis via the PI3K-AKT signaling pathway and ECM-receptor interaction. In vivo results have proven that treatment with biomimetic peptide nanonets can alleviate systemic bacterial infections without causing noticeable systemic toxicity. As anticipated, the proposed strategy can address stubborn infections by entrapping bacteria and awakening antibacterial immune responses. This approach might serve as a guide for the design of bioinspired materials for future clinical applications.

Design of Proteolytic-Resistant Antifungal Peptides by Utilizing Minimum d-Amino Acid Ratios

Antifungal peptides are an appealing alternative to standard antifungal medicines due to their unique mechanism of action and low-level resistance. However, their susceptibility to protease degradation keeps hindering their future development. Herein, a library was established to design peptides with protease resistance and high antifungal activity. The peptides were incorporated with minimal D-amino acids to further improve the protease stability. The most active peptide, IR3, demonstrated good antifungal activity and low toxicity, and its molecular integrity was maintained after protease hydrolysis for 8 h at 2 mg/mL. Furthermore, IR3 could permeate the fungal cell wall, disrupt the cell membrane, produce reactive oxygen species, and induce apoptosis in fungal cells. In vivo experiments confirmed that IR3 could effectively treat fungal keratitis. Collectively, these findings suggest that IR3 is a promising antifungal agent and may be beneficial in the design and development of protease-resistant antifungal peptides.

Unlocking Antibacterial Potential: Key-Site-Based Regulation of Antibacterial Spectrum of Peptides

In the pursuit of combating multidrug-resistant bacteria, antimicrobial peptides (AMPs) have emerged as promising agents; however, their application in clinical settings still presents challenges. Specifically, the exploration of crucial structural parameters that influence the antibacterial spectrum of AMPs and the subsequent development of tailored variants with either broad- or narrow-spectrum characteristics to address diverse clinical therapeutic needs has been overlooked. This study focused on investigating the effects of amino acid sites and hydrophobicity on the peptide's antibacterial spectrum through Ala scanning and fixed-point hydrophobic amino acid substitution techniques. The findings revealed that specific amino acid sites played a pivotal role in determining the antibacterial spectrum of AMPs and confirmed that broadening the spectrum could be achieved only by increasing hydrophobicity at certain positions. In conclusion, this research provided a theoretical basis for future precise regulation of an antimicrobial peptide's spectrum by emphasizing the intricate balance between amino acid sites and hydrophobicity.

Engineered Peptides Harboring Cation Motifs Against Multidrug-Resistant Bacteria

Multidrug-resistant (MDR) pathogens pose a serious threat to the health and life of humans, necessitating the development of new antimicrobial agents. Herein, we develop and characterize a panel of nine amino acid peptides with a cation end motif. Bioactivity analysis revealed that the short peptide containing "RWWWR" as a central motif harboring mirror structure "KXR" unit displayed not only high activity against MDR planktonic bacteria but also a clearance rate of 92.33% ± 0.58% against mature biofilm. Mechanically, the target peptide (KLR) killed pathogens by excessively accumulating reactive oxygen species and physically disrupting membranes, thereby enhancing its robustness for controlling drug resistance. In the animal model of sepsis infection by MDR bacteria, the peptide KLR exhibited strong therapeutic effects. Collectively, this study provided the dominant structure of short antimicrobial peptides (AMPs) to replenish our arsenals for combating bacterial infections and illustrated what could be harnessed as a new agent for fighting MDR bacteria.

Antimicrobial peptides in combination with citronellal efficiently kills multidrug resistance bacteria

BACKGROUND

Antimicrobial peptides (AMPs) are considered as the most potential alternatives to antibiotics, but they have several drawbacks, including high cost, medium antimicrobial efficacy, poor cell selectivity, which limit clinical application. To overcome the above problems, combination therapy of AMPs with adjuvants might maximize the effectiveness of AMPs. We found that citronellal can substantially potentiate the ZY4R peptide efficacy against Escherichia coli ATCC25922. However, it is unclear whether ZY4R/citronellal combination poses synergistic antimicrobial effects against most bacteria, and their synergy mechanism has not been elucidated.

PURPOSE

To investigate synergistic antimicrobial efficacies, biosafety, and synergy mechanism of ZY4R/citronellal combination.

METHOD

Checkerboard, time-kill curves, cytotoxicity assays, and in vivo animal models were conducted to assess synergistic antimicrobial effects and biosafety of the ZY4R/citronellal combination. To evaluate their synergy mechanism, a series of cell-based assays and transcriptome analysis were performed.

RESULTS

ZY4R/citronellal combination exhibited synergistic antimicrobial effects against 20 clinically significant pathogens, with the fractional inhibitory concentration index (FICI) ranging from 0.313 to 0.047. Meanwhile, ZY4R/citronellal combination enhanced antimicrobial efficacies without compromising cell selectivity, contributing to decreasing drug dosage and improving biosafety. Compared with ZY4R (4 mg/kg) and citronellal (25 mg/kg) alone, ZY4R (4 mg/kg)/citronellal (25 mg/kg) combination significantly decreased the bacterial load in peritoneal fluid, liver, and kidney (P < 0.05) and alleviated pathological damage of the organs of mice. Mechanistic studies showed that ZY4R allowed citronellal to pass through the outer membrane rapidly and acted on the inner membrane together with citronellal, causing more potent membrane damage. The membrane damage prompted the continuous accumulation of citronellal in cells, and citronellal further induced energy breakdown and inhibited exopolysaccharide (EPS) production, which aggravated ZY4R-induced outer membrane damage, thereby resulting in bacterial death.

CONCLUSIONS

ZY4R/citronellal combination exhibited broad-spectrum synergy with a low resistance development and high biosafety. Their synergy mechanism acted on two important cellular targets (energy metabolism and membrane integrity). Combination therapy of ZY4R with citronellal may be a promising mixture to combat bacterial infections facing an antibiotic-resistance crisis.

Multivalency-enhanced enzyme inhibitors with biomolecule-responsive activity

This work reports a polymeric adenosine triphosphate (ATP)-responsive trypsin inhibitor. The polymeric inhibitor was rationally obtained by optimizing the benzamidine and phenylboronic acid monomers, which could synergistically bind with the phosphate and ribose groups in ATP. The ATP-responsive trypsin activity shows its potential as a therapeutic drug for cancer-targeting cell inhibition.

Ultrashort All-Hydrocarbon Stapled α-Helix Amphiphile as a Potent and Stable Antimicrobial Compound

The ravaging effect of drug-resistant bacteria has heightened the need for the development of membrane-soluble antimicrobial peptides (AMPs). However, their potential for clinical use is hindered by issues such as poor biocompatibility, salt sensitivity, and proteolytic lability. In this study, a series of ultrashort stapled cyclization heptapeptides were obtained by inserting all-hydrocarbon staples. StRRL with the highest therapeutic index (TI = 36.3) was selected after evaluating its antibacterial and toxic activity. Furthermore, stRRL demonstrated exceptional performance in high-protease and high-salt environments, making it an effective weapon against bacteria like Escherichia coli in a mouse peritonitis-sepsis model. The membrane lytic mechanism of stRRL, which operates from outside to inside, gives it a low drug-resistant tendency. This suggests that stRRL has the potential to replace antibiotics as a powerful candidate in tackling bacterial infection. In conclusion, the ultrashort all-hydrocarbon stapled antimicrobial amphiphiles inaugurated a novel entrance to the advancements of highly stable peptide compounds.

Protein Transduction System Based on Tryptophan-zipper against Intracellular Infections via Inhibiting Ferroptosis of Macrophages

Cells penetrating molecules in living systems hold promise of capturing and eliminating threats and damage that can plan intracellular fate promptly. However, it remains challenging to construct cell penetration systems that are physiologically stable with predictable self-assembly behavior and well-defined mechanisms. In this study, we develop a core-shell nanoparticle using a hyaluronic acid (HA)-coated protein transduction domain (PTD) derived from the human immunodeficiency virus (HIV). This nanoparticle can encapsulate pathogens, transporting the PTD into macrophages via lipid rafts. PTD forms hydrogen bonds with the components of the membrane through TAT, which has a high density of positive charges and reduces the degree of membrane order through Tryptophan (Trp)-zipper binding to the acyl tails of phospholipid molecules. HA-encapsulated PTD increases the resistance to trypsin and proteinase K, thereby penetrating macrophages and eliminating intracellular infections. Interestingly, the nonagglutination mechanism of PTD against pathogens ensures the safe operation of the cellular system. Importantly, PTD can activate the critical pathway of antiferroptosis in macrophages against pathogen infection. The nanoparticles developed in this study demonstrate safety and efficacy against Gram-negative and Gram-positive pathogens in three animal models. Overall, this work highlights the effectiveness of the PTD nanoparticle in encapsulating pathogens and provides a paradigm for transduction systems-anti-intracellular infection therapy.

Boosting stability and therapeutic potential of proteolysis-resistant antimicrobial peptides by end-tagging β-naphthylalanine

Recently, much emphasis has been placed on solving the intrinsic defects of antimicrobial peptides (AMPs), especially their susceptibility to protease digestion for the systemic application of antibacterial biomaterials. Although many strategies have increased the protease stability of AMPs, antimicrobial activity was severely compromised, thereby substantially weakening their therapeutic effect. To address this issue, we introduced hydrophobic group modifications at the N-terminus of proteolysis-resistant AMPs D1 (AArIIlrWrFR) through end-tagging with stretches of natural amino acids (W and I), unnatural amino acid (Nal) and fatty acids. Of these peptides, N1 tagged with a Nal at N-terminus showed the highest selectivity index (GM_SI = 19.59), with a 6.73-fold improvement over D1. In addition to potent broad-spectrum antimicrobial activity, N1 also exhibited high antimicrobial stability toward salts, serum and proteases in vitro and ideal biocompatibility and therapeutic efficacy in vivo. Furthermore, N1 killed bacteria through multiple mechanisms, involving disruption of bacterial membranes and inhibition of bacterial energy metabolism. Indeed, appropriate terminal hydrophobicity modification opens up new avenues for developing and applying high-stability peptide-based antibacterial biomaterials. STATEMENT OF SIGNIFICANCE: To improve the potency and stability of proteolysis-resistant antimicrobial peptides (AMPs) without increasing toxicity, we constructed a convenient and tunable platform based on different compositions and lengths of hydrophobic end modifications. By tagging an Nal at the N-terminal, the obtained target compound N1 exhibited strong antimicrobial activity and desirable stability under multifarious environments in vitro (protease, salts and serum), and also showed favorable biocompatibility and therapeutic efficacy in vivo. Notably, N1exerted its bactericidal effect by damaging bacterial cell membranes and inhibiting bacterial energy metabolism in a dual mode. The findings provide a potential method for designing or optimizing proteolysis-resistant AMPs thus promoting the development and application of peptide-based antibacterial biomaterial.

Characterization of simplified nonapeptides with broad-spectrum antimicrobial activities as potential food preservatives, and their antibacterial mechanism

Antimicrobial peptides (AMPs) have attracted attention in the field of food preservatives due to their favorable biosafety and potential antimicrobial activity. However, high synthetic cost, systemic toxicity, a narrow antimicrobial spectrum, and poor antimicrobial activity become the main bottlenecks for their practical applications. To address these questions, a set of derived nonapeptides were designed based on a previously discovered ultra-short peptide sequence template (RXRXRXRXL-NH₂) and screened to identify an optimal peptide-based food preservative with excellent antimicrobial properties. Among these nonapeptides, the designed peptides 3IW (RIRIRIRWL-NH₂) and W2IW (RWRIRIRWL-NH₂) presented a membrane-disruptive and reactive oxygen species (ROS) accumulation mechanism to execute potent and rapid broad-spectrum antimicrobial activity without observed cytotoxicity. Moreover, they exhibited favorable antimicrobial stability regardless of high ionic strength, heat, and excessive acid-base conditions, retaining potent antimicrobial effects for chicken meat preservation. Collectively, their ultra-short sequence length and potent broad-spectrum antimicrobial capacity may be beneficial for the further development of green and safe peptide-based food preservatives.

Hydrophobic modification improves the delivery of cell-penetrating peptides to eliminate intracellular pathogens in animals

Infections induced by intracellular pathogens are difficult to eradicate due to poor penetration of antimicrobials into cell membranes. It is of great importance to develop a new generation of antibacterial agents with dual functions of efficient cell penetration and bacterial inhibition. In this study, the association between hydrophobicity and cell-penetrating peptide delivery efficiency was investigated by fragment interception and hydrophobicity modification of natural porcine antimicrobial peptide PR-39 and the combination of cationic cell-penetrating peptide (R6) with antimicrobial peptide fragments modified with hydrophobic residues. The chimeric peptides P3I7 and P3L7, obtained through biofunctional screening, exhibited potent broad-spectrum antibacterial activity and low cytotoxicity. Moreover, P3I7 and P3L7 can effectively penetrate cells to eliminate intracellular pathogens mainly through endocytosis. The membrane destruction mechanism makes the peptides fast sterilizers and less prone to developing drug resistance. Finally, their good biocompatibility and antibacterial infection effects were verified in mice and piglets. To conclude, the chimeric peptides P3I7 and P3L7 show great potential as affordable and effective antimicrobial agents and may serve as ideal candidates for the treatment of intracellular bacterial infections. STATEMENT OF SIGNIFICANCE: The low permeability of antibacterial drugs makes infections induced by intracellular bacteria extremely difficult to treat. To address this issue, we designed chimeric peptides with dual cell-penetrating and antibacterial functions. The active peptides P3I7 and P3L7, acquired through functional screening have strong broad-spectrum antibacterial activity and powerful bactericidal effects against intracellular Staphylococcus aureus. The membrane permeation mechanism of P3I7 and P3L7 against bacteria endows fast bactericidal activity with low drug resistance. The biosafety and antibacterial activity of P3I7 and P3L7 were also validated by in vivo trials. This study provides an ideal drug candidate against intracellular bacterial infections.

Self-Assembly of Antimicrobial Peptide-Based Micelles Breaks the Limitation of Trypsin

Targeting the limitation of antimicrobial peptides (AMPs) application in vivo, self-assembled AMPs library with specific nanostructures is expected to gradually overtake monomer AMPs libraries in the future. Peptide polymers are fascinating self-assembling nanoscale structures that have great advantage in biomedical applications because of their satisfactory biocompatibility and versatile properties. Herein, we describe a strategy for inducing the self-assembly of T9W into nanostructured antimicrobial micelles with evidently improved pharmacological properties, that is, PEGylation at the C-terminal of T9W (CT9W₁₀₀₀), an antibacterial biomaterial that self-assembles in aqueous media without exogenous excipients, has been developed. Compared with parental molecular, the CT9W₁₀₀₀ is more effective against Pseudomonas aeruginosa, and its antibacterial spectrum had also been broadened. Additionally, CT9W₁₀₀₀ micelles had higher stability under salt ion, serum, and acid-base environments. Importantly, the self-assembled structure is highly resistant to trypsin degradation, probably allowing T9W to be applied in clinical settings in the future. Mechanistically, by acting on membranes and through supplementary bactericidal mechanisms, CT9W₁₀₀₀ micelles contribute to the antibacterial process. Collectively, CT9W₁₀₀₀ micelles exhibited good biocompatibility in vitro and in vivo, resulting in highly effective treatment in a mouse acute lung injury model induced by P. aeruginosa PAO1 without drug resistance. These advances may profoundly accelerate the clinical transformation of T9W and promote the development of a combination of peptide-based antibiotics and PEGylated nanotechnology.

Gut-Derived Metabolites from Dietary Tryptophan Supplementation Quench Intestinal Inflammation through the AMPK-SIRT1-Autophagy Pathway

Tryptophan has drawn wide attention due to its involvement in improving intestinal immune defense directly and indirectly by regulating metabolic pathways. The study aims to elucidate the potential modulating roles of tryptophan to protect against intestinal inflammation and elucidate the underlying molecular mechanisms. The protective effects of tryptophan against intestinal inflammation are examined in the lipopolysaccharide (LPS)-induced inflammatory model. We first found that tryptophan markedly (p < 0.01) inhibited proinflammatory cytokines production and nuclear factor κB (NF-κB) pathway activation upon LPS challenge. Next, we demonstrated that tryptophan (p < 0.05) attenuated LPS-caused intestinal mucosal barrier damage by increasing the number of goblet cells, mucins, and antimicrobial peptides (AMPs) in the ileum of mice. In addition, tryptophan (p < 0.05) inhibited LPS-induced autophagic flux through the AMP-activated protein kinase (AMPK)-sirtuin 1 (SIRT1) pathway in the intestinal systems to maintain autophagy homeostasis. Meanwhile, tryptophan also reshaped the gut microbiota composition in LPS-challenge mice by increasing the abundance of short-chain fatty acid (SCFA)-producing bacteria such as Acetivibrio (0.053 ± 0.017 to 0.21 ± 0.0041%). Notably, dietary tryptophan resulted in the activation of metabolic pathways during the inflammatory response. Furthermore, exogenous treatment of tryptophan metabolites kynurenine (Kyn) and 5-HT in porcine intestinal epithelial cells (IPEC-J2 cells) reproduced similar protective effects as tryptophan to attenuate LPS-induced intestinal inflammation through regulating the AMPK-SIRT1-autophagy. Taken together, the present study indicates that tryptophan exhibits intestinal protective and immunoregulatory effects resulting from the activation of metabolic pathways, maintenance of gut mucosal barrier integrity, microbiota composition, and AMPK-SIRT1-autophagy level.