A mouse study tracks how a leading GLP-1 drug alters gut bacteria over time, offering new clues to whether microbiome changes linger after dosing ends.
Study: Effects of liraglutide on gut bacterial community dynamics. Image Credit: CI Photos / Shutterstock
In a recent study published in the journal Microbiology Spectrum, researchers used male diet-induced obese mice to investigate the effects of daily liraglutide administration on gut bacterial community dynamics. They analyzed fecal samples collected at three time points during a 21-day intervention and washout protocol.
The analysis showed that liraglutide selectively increased taxa related to lactic acid-producing bacteria while suppressing several protein- and carbohydrate-fermenting taxa. These changes were found to be rapid and largely, although not completely, reversible during the seven-day washout period. However, the study did not determine whether these microbial shifts benefited or harmed gut health.
Background
Decades of metabolic research have established a close physiological link between obesity and its associated cardiometabolic comorbidities, as well as subsequent alterations in the composition of the gut bacterial community.
The relatively recent introduction of glucagon-like peptide-1 receptor agonists (GLP-1 RAs) has substantially expanded the pharmacological treatment of these metabolic conditions. However, their effects on gut bacterial composition and function remain poorly understood.
While human clinical trials have demonstrated liraglutide’s clinical efficacy and characterized its safety profile, preclinical evidence remains limited regarding whether GLP-1 RAs induce lasting structural alterations in the gut microbiota.
Furthermore, since previous GLP-1 RA investigations have recorded microbial shifts following GLP-1 RA administration, it remains unclear whether these shifts represent transient pharmacological responses that normalize following a drug washout period or persist after treatment withdrawal.
About the Study
The present study aimed to address these microbial uncertainties by using male C57BL/6J diet-induced obese (DIO) mice to track longitudinal shifts in gut bacterial diversity and composition over a 21-day period.
Researchers monitored 24 mice with eight animals in each of three treatment arms: 1. High-fat diet with daily subcutaneous liraglutide injections (0.2 mg/kg) for 14 days followed by a 7-day drug washout (HFL), 2. High-fat diet control receiving daily phosphate-buffered saline (PBS) vehicle injections (HFC), and 3. Low-fat diet control receiving the same vehicle injections (LFC). The body weights of all experimental animals were recorded daily throughout the trial. Food was weighed daily, but intake could not be analyzed because the high-fat-fed mice frequently shredded their food.
Bacterial community dynamics were evaluated using mouse-derived fecal DNA extracted at baseline (Day 0), post-treatment (Day 14), and post-washout (Day 21). Fecal DNA was sequenced using high-throughput Illumina paired-end sequencing, which specifically targeted the V4-V5 region of the bacterial 16S ribosomal ribonucleic acid (rRNA) gene, thereby yielding approximately 7.1 million high-quality reads.
Downstream bioinformatics analyses used non-metric multidimensional scaling (NMDS), an ordination method based on Bray-Curtis dissimilarities, to assess shifts in community structure. Additionally, a Similarity Percentages (SIMPER) analysis was used to identify distinct bacterial DNA sequence types, known as amplicon sequence variants (ASVs), that contributed most strongly to the observed community differences.
Study Findings
The results showed that liraglutide reduced body weight in HFL mice, which weighed significantly less than HFC controls by Day 4, while the HFC group continued to gain weight. Notably, following the cessation of daily liraglutide administration on Day 14, HFL animals were observed to experience a gradual rebound in body weight through Day 21, although they remained significantly lighter than HFC controls. This indicated partial reversal of the treatment-associated weight loss after withdrawal.
Ecological analyses of the fecal bacterial community revealed distinct structural shifts in experimental mice during active treatment. For example, non-metric multidimensional scaling (NMDS) ordination showed clear separation of the bacterial community structure of HFL mice on Day 14 from their baseline (Day 0) readings and from the control groups, HFC and LFC, with statistical analyses indicating significant differences.
However, the study found that after the 7-day washout period on Day 21, the gut bacterial community of HFL mice shifted back toward its baseline structure and converged with that of vehicle-treated HFC animals, while remaining significantly different from the LFC group. Shannon diversity and Chao1 species richness corroborated these findings and further revealed a temporary decline during active treatment. Shannon diversity recovered only partially, while Chao1 richness returned to approximately its baseline level after washout. Bacteroidales-related sequences also remained reduced at Day 21.
Finally, the SIMPER analysis identified 21 primary ASVs, accounting for 83% of the community variation within the HFL group. The analyses demonstrated that nine ASVs increased significantly during active treatment: six were closely related to Lactobacillus gasseri, L. paragasseri, and L. johnsonii, while three were closely related to Leptogranulimonas caecicola.
Conversely, 12 ASVs associated with protein- and carbohydrate-fermenting taxa, including the genera Romboutsia, Faecalicatena, and Oscillibacter, were observed to decline significantly by Day 14, from 11.49% to 2.61%, before partially recovering to 8.54% post-washout on Day 21.
Conclusions
The present study shows that liraglutide was associated with rapid and largely reversible changes in the fecal bacterial community of male high-fat-fed mice.
While these results were derived from exclusively male mice and cannot be directly generalized to human cohorts, the findings suggest that liraglutide temporarily favored taxa related to mucin- and bile acid-associated lactic acid bacteria while reducing several fermentative taxa. However, the study did not directly measure mucin, bile acids, bacterial metabolism, or the mechanisms responsible for these changes, and it remains unknown whether similar effects occur in humans. Because liraglutide was administered only to high-fat-fed mice, the study also could not determine whether the microbial response differed by diet.
The study advances scientific understanding of the transient host-microbiome interactions during liraglutide interventions and offers a foundation for investigating how these microbial shifts may relate to the metabolic and gastrointestinal effects of GLP-1 RA therapy.
Longer-term studies incorporating female animals, measuring or controlling food intake, performing functional microbial analyses, using higher-resolution sequencing, and including human cohorts are needed to establish the persistence, causes, and clinical relevance of these changes.
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