This pilot study investigates whether fecal microbiota transplantation (FMT) can modify the gut microbiome in patients with type 2 diabetes mellitus and stable coronary artery disease (CAD).

Type 2 diabetes and CAD are closely linked metabolic and inflammatory conditions associated with substantial morbidity and mortality. Emerging evidence suggests that the gut microbiome plays an important role in metabolic regulation, systemic inflammation, and cardiovascular disease. Alterations in gut microbial composition have been associated with insulin resistance, dyslipidemia, and atherosclerosis. Modulation of the gut microbiome therefore represents a promising investigational therapeutic strategy.

FMT is an established medical procedure involving the transfer of processed stool from a carefully screened healthy donor into the gastrointestinal tract of a recipient with the aim of altering the gut microbial ecosystem. FMT has demonstrated clinical efficacy in specific indications and is generally considered safe when performed under standardized conditions with rigorous donor screening.

In this prospective, single-arm, single-center pilot study, eligible patients with type 2 diabetes and stable CAD will undergo FMT administered via colonoscopy. The primary objective is to evaluate whether FMT induces measurable changes in gut microbiome composition six months following the intervention. Secondary objectives include assessment of temporal microbiome dynamics at earlier time points, as well as evaluation of potential effects on the oral microbiome, metabolic parameters, lipid profile, glucose homeostasis, inflammatory biomarkers, and vascular function.

Participants will be monitored throughout the study period for safety and tolerability. The study is designed to evaluate feasibility, characterize microbiome alterations, and explore potential biological effects rather than to demonstrate definitive clinical efficacy.

This study is conducted at the University Hospital Zurich. The results may contribute to a better understanding of the relationship between the gut microbiome, metabolic regulation, inflammation, and cardiovascular disease, and may inform the design of future randomized clinical trials.

Type 2 diabetes mellitus and coronary artery disease (CAD) represent highly prevalent and closely interconnected chronic conditions characterized by metabolic dysregulation, systemic inflammation, and increased cardiovascular risk. Despite advances in medical therapy, morbidity and mortality associated with CAD remain substantial, highlighting the need for improved understanding of underlying pathophysiological mechanisms and novel therapeutic strategies.

Recent research has identified the gut microbiome as a potentially important contributor to metabolic homeostasis, immune regulation, and cardiovascular disease. Alterations in gut microbial composition and function have been associated with insulin resistance, impaired glucose metabolism, lipid abnormalities, and chronic low-grade inflammation. Furthermore, microbiome-derived metabolites have been implicated in pathways relevant to atherosclerosis development and progression. These findings suggest that targeted modulation of the gut microbiome may represent a biologically plausible approach to influence metabolic and inflammatory processes relevant to both diabetes and cardiovascular disease.

Fecal microbiota transplantation (FMT) is a medical procedure designed to modify the gut microbial ecosystem through the transfer of processed stool from a carefully screened healthy donor into the gastrointestinal tract of a recipient. FMT has demonstrated clinical efficacy in specific indications and has been increasingly investigated for its broader biological effects on host metabolism and immune function. While FMT is primarily established in other clinical contexts, its potential impact on cardiometabolic disease mechanisms remains incompletely understood.

This pilot study is designed to investigate whether FMT can induce measurable alterations in gut microbiome composition in patients with type 2 diabetes mellitus and stable CAD. The study further aims to characterize the temporal dynamics of microbiome changes following FMT and to explore potential associations between microbiome modulation and surrogate markers of metabolic regulation, systemic inflammation, and vascular function. In addition, potential effects on the oral microbiome will be evaluated, reflecting growing recognition of the interplay between different microbial ecosystems.

The study follows a prospective, single-arm design to assess feasibility and biological effects in a well-defined patient population. FMT will be administered via colonoscopy according to established clinical procedures and institutional standards. Colonoscopic administration is selected to ensure standardized delivery of the microbiota preparation directly into the colon.

This investigation is exploratory in nature. It is not designed or powered to demonstrate definitive clinical efficacy, but rather to evaluate feasibility, characterize microbiome responses, and generate mechanistic insights that may inform future hypothesis-driven randomized clinical trials. Particular emphasis is placed on describing the magnitude, variability, and time course of microbiome alterations following FMT in this patient population.

Participants will undergo longitudinal assessments of gut microbiome composition, oral microbiome composition, metabolic parameters, inflammatory biomarkers, and vascular function. These measurements are intended to provide an integrated characterization of biological responses potentially associated with microbiome modulation.

FMT is generally considered safe when performed under standardized conditions with rigorous donor screening. Donor selection and screening procedures will be conducted in accordance with institutional protocols and current safety standards. Participants will be monitored throughout the study period for safety and tolerability, including procedure-related and microbiota-related adverse events.

This study is conducted at the University Hospital Zurich. The findings may contribute to a better understanding of the gut microbiome in cardiometabolic disease and may support the design of future interventional studies targeting microbiome-related mechanisms.

Inclusion Criteria (Recipients):

Age ≥18 years and ≤75 years Diagnosis of type 2 diabetes mellitus Stable coronary artery disease Platelet count ≥50 × 10⁹/L within 2 days prior to FMT Hemoglobin ≥8.5 g/dL within 2 days prior to FMT International normalized ratio (INR) ≤1.5 within 2 days prior to FMT Willingness to undergo fecal microbiota transplantation (FMT) via colonoscopy Signed informed consent

Exclusion Criteria (Recipients):

Pregnancy or breastfeeding Women of childbearing potential not using adequate contraception Acute coronary syndrome within 12 months Requirement for dual antiplatelet therapy Relevant moderate or severe valvular heart disease Severe kidney dysfunction (estimated GFR <30 mL/min) Significant liver dysfunction Contraindications to colonoscopy or FMT Systemic steroid or immunosuppressive therapy Antibiotic therapy within 3 months Ongoing infectious disease Active malignancy Participation in another interventional study Life expectancy <12 months Inability to provide informed consent

Inclusion Criteria (Donors):

Healthy participants ≥18 years and <60 years Eligibility for stool donation according to institutional donor screening procedures Negative donor screening results Signed informed consent

Exclusion Criteria (Donors):

History of gastrointestinal disease History of metabolic, autoimmune, or chronic inflammatory disease History of infectious disease Recent antibiotic therapy High-risk behavior for transmissible diseases Contraindications to colonoscopy Pregnancy or breastfeeding