Table 1.
Summary of studies related to bacterial metabolites and their role in AD homeostasis.
| Author | Metabolite or Microbe | Gut or Skin Microbiota | Findings/Conclusion |
|---|---|---|---|
| Chng et al. [20] | Tryptophan | Skin | Metagenome analysis revealed attenuation of Trp metabolic pathway in AD patients |
| Yu et al. [16] | Indole-3-aldehyde (Trp derivative) | Skin | Trp metabolites of skin microbiota play a significant functional role in AD and IAId induced AhR interactions may promote skin immune homeostasis |
| Liu et al. [25] | Indole-3-aldehyde (Trp derivative) | Skin | IAId activation of AhR in LCs inhibit CD4+ T cell proliferation and induce IL-10 production and immune tolerance |
| Nakatsuji et al. [43] | Staphlococcus hominus | Skin | Bacteriotherapy with CoNS may help restablish commensal bacterial metabolites to protect against S. aureus |
| Traisaeng et al. [29] | Butyric acid | Skin | Production of butyric acid derivatives by S. epidermidis inhibit growth of S. aureus in AD patients |
| Wang et al. [35] | Propionic acid | Skin | Propionic acid and its esterified derivative provide efficacy as antimicrobial agents against AD S. aureus |
| Myles et al. [52] | R. mucosa & sphingomyelins | Skin | Topical treatment was associated with amelioration of disease severity, improvement in barrier function, and reduction in both S. aureus and need for topical steroids |
| Myles et al. [53] | R. mucosa & sphingomyelins | Skin | Mouse models of AD found production of sphingolipids by R. mucosa, cholinergic signaling, and flaggelin expression may contribute to therapeutic impact in the previous trial [52] |
| Kim et al. [60] | Lactobacillus spp. for production of multiple metabolites | Gut | Administration of probiotic microorganisms reduced inflammatory immune responses associated with AD and increased levels of amino acids and SCFAs |
| Matsumoto et al. [65] | Fecal spermidine and butyrate | Gut | Bifidobacterium animalis in yogurt improved scores of itch and burning and significantly increased IFN-y serum levels |
| Kim et al. [72] | FMT | Gut | FMT resulted in an increase in levels of SCFAs as gut metabolites and decreases in blood parameters suggested of AD-induced allergic responses with suggested prolonged efficacy compared to probiotics |
| Hou et al. [73] | IL-37b cytokine | Gut | IL-37b restored gut dysbiosis in terms of diversity and could ameliorate eosinophil-mediated allergic inflammation via intestinal bacteria and metabolite modulation |
| Chu et al. [76] | Lytic crAssphage viral strains | Gut | Gut virome phage alterations manipulate gut bacterial production of aromatic amino acids and AD symptoms |