Advances in Gut Microbiome Research in T1D
Lente Blok, Nordin Hanssen, Max Nieuwdorp and Elena Rampanelli
From Microbes to Metabolites: Advances in Gut Microbiome Research in Type 1 Diabetes. Metabolites. 2025 Feb 19;15(2):138.
Type 1 diabetes (T1D) is a severe autoimmune disease affecting approximately 12.7 million people worldwide, with incidence rising at 3–5% per year. While genetic factors play an important role, they cannot fully explain this increase — fewer than 10% of individuals with high-risk genotypes develop T1D, and concordance rates in identical twins remain below 50%. This points to a critical role for environmental factors. Among these, the gut microbiome has emerged as a key area of investigation. This review, conducted by researchers from Diabeter Center Amsterdam / Amsterdam UMC and the Amsterdam Institute for Infection and Immunity, synthesises current observational, mechanistic and interventional evidence on the role of the gut microbiome and its metabolites in T1D pathogenesis and treatment.
The review draws on data from major longitudinal cohort studies including TEDDY, DIABIMMUNE, ABIS, DIPP and INNODIA, as well as a range of human intervention trials evaluating prebiotics, probiotics, synbiotics, postbiotics and fecal microbiota transplantation (FMT).
Key findings:
- Characteristic microbiome alterations precede and accompany T1D: Across multiple studies, T1D is consistently associated with increased abundance of Bacteroidetes, reduced levels of short-chain fatty acid (SCFA)-producing bacteria such as Faecalibacterium prausnitzii, Bifidobacterium and Lactobacillus species, and a depletion of Akkermansia at disease onset. Importantly, many of these changes are detectable before clinical diagnosis — including before seroconversion to islet autoimmunity.
- Microbial metabolites are key mediators of immune regulation: Three metabolite classes are particularly implicated in T1D pathogenesis. SCFAs — primarily acetate, propionate and butyrate — support gut barrier integrity, promote regulatory T cell (Treg) differentiation and suppress pro-inflammatory cytokine production, with reduced SCFA levels consistently found in children who develop T1D. Tryptophan metabolites, produced via the kynurenine and indole pathways, modulate immune tolerance and intestinal homeostasis, and are significantly depleted in T1D patients. Secondary bile acids, dysregulated in children as early as 18–24 months before islet autoimmunity, influence Treg and Th17 cell differentiation and glucose metabolism.
- Intestinal barrier dysfunction is an early and recurrent feature: Increased gut permeability — the so-called "leaky gut" — is observed at the stage of islet autoimmunity, prior to clinical diagnosis, and persists in long-standing T1D. This allows bacterial products to engage the immune system and potentially trigger or amplify autoimmune responses targeting pancreatic beta cells.
- Molecular mimicry offers a mechanistic link between gut microbes and autoimmunity: Several gut microbes express peptides that structurally resemble beta cell autoantigens, and can activate cross-reactive autoreactive T cells. For example, a peptide from Parabacteroides distasonis shares over 50% homology with the insulin B-chain sequence and activates HLA-DQ8 CD4+ T cells from T1D patients. Colonisation with P. distasonis accelerated T1D development in NOD mice.
- Microbiome-based interventions show promise but require further investigation: Early probiotic supplementation was associated with a 34% reduction in islet autoimmunity risk in genetically susceptible children in the TEDDY study. In children with new-onset T1D, a 6-month course of VIVOMIXX® significantly preserved C-peptide levels and reduced HbA1c, accompanied by increased Tregs and IL-10. FMT halted progression of new-onset T1D in a randomised controlled trial, with autologous FMT preserving C-peptide levels at 12 months. SCFA delivery via modified dietary starch (HAMSAB) promoted immune tolerance and shifted T and B cell phenotypes towards regulatory profiles, though effects on glycaemia and beta cell function were limited — particularly in patients with long-standing disease, suggesting that the timing of intervention is critical.
- Translation from animal models to humans remains challenging: While many interventions have shown striking results in NOD mice, human trials have yielded more modest outcomes. The authors highlight that the NOD mouse model incompletely replicates the complexity of human T1D, that disease heterogeneity is greater in humans, and that the timing of intervention — ideally early in life or at the stage of autoimmunity — is likely decisive.
This review provides a comprehensive synthesis of current evidence linking the gut microbiome to T1D pathogenesis and highlights the growing therapeutic potential of microbiome-targeted strategies. The authors call for larger longitudinal studies, meta-analyses, and a personalised medicine approach to translate these findings into effective prevention and treatment strategies for human T1D.
Concluding, the authors state
"A deeper understanding of the evolution of the gut microbiome before and after T1D onset and of the microbial signals conditioning host immunity may provide us with essential insights for exploiting the microbiome as a prognostic and therapeutic tool."
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