In a recent study published in Clinical Microbiology, a team of researchers delved into the relationship between gut microbiota, metabolite changes, and immune function during pregnancy. They compared the gut microbiota, fecal and plasma metabolites, and cytokines in pregnant and non-pregnant women.
Background:
Pregnancy brings about significant changes in hormonal levels, body structure, and immune function, all crucial for the development of the fetus. Initially, the maternal immune system is pro-inflammatory, transitioning to an anti-inflammatory state, and then reverting to a pro-inflammatory state to initiate labor.
The role of the gut microbiome in regulating immunity during pregnancy is increasingly acknowledged, with studies demonstrating its impact on pregnancy outcomes and conditions like preeclampsia through alterations in microbial composition and interactions with immune cells. However, the detailed mechanisms remain unclear. Metabolites, rather than direct microbial interactions, primarily mediate the connection between the microbiome and the immune system, indicating the need for further research to comprehend pregnancy-related immune adjustments and devise new therapeutic approaches.
About the study:
The study, conducted at the First Affiliated Hospital of Jinan University from February 2019 to August 2020, involved 30 pregnant and 15 non-pregnant women. Its aim was to explore the interactions between gut microbiota, metabolites, and immune function.
Pregnant participants, aged 18 to 34 years, with naturally conceived singleton pregnancies and a pre-pregnancy BMI of 18.5 to 21.9 kg/m2, were recruited. Those with pregnancy complications or immune disorders were excluded. The control group comprised healthy females matched in age and BMI to the pregnant group, with neither group using probiotics or antibiotics six months before the study.
Fecal and blood samples were collected from pregnant women in late third trimester and non-pregnant women on the 14th day of their menstrual cycle. Fecal samples were collected using sterile techniques and stored at -80°C, while blood samples were processed to separate serum and stored under the same conditions.
The study utilized 16S ribosomal RNA (rRNA) gene sequencing to analyze gut microbiota, with DNA extraction and sequencing used to identify microbial species. Random forest analysis and Weighted Gene Co-expression Network Analysis (WGCNA) were employed to differentiate microbial profiles between groups.
Untargeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) metabolomics analyzed fecal and plasma samples to identify metabolic changes, with quality control measures ensuring data reliability. Metabolomic data were processed and analyzed to determine significant differences and map them to biological pathways using the Kyoto Encyclopedia of Genes and Genomes (KEGG) database.
Plasma cytokines were measured using a multiplex bead assay to assess immune function differences between groups. Finally, statistical and visualization tools were used for multi-omics analysis to integrate data from microbial, metabolomic, and cytokine analyses to explore potential correlations and mediation effects.
Study results:
The study found no significant differences in average age or pre-pregnancy BMI between the two groups. Immune profiling revealed that pregnant participants had lower levels of pro-inflammatory cytokines and higher levels of certain anti-inflammatory cytokines than controls, indicating a shift towards immunosuppression during pregnancy.
Distinct microbial compositions were found between pregnant and non-pregnant women, with pregnant women exhibiting higher operational taxonomic unit (OTU) diversity and differences in bacterial phyla abundance. Certain gut bacteria groups were identified to have consistent effects in reducing inflammation during pregnancy.
Metabolomic analysis revealed significant metabolic alterations during pregnancy, particularly in lipids and bile acids, with many downregulated metabolites identified. Correlation studies suggested that certain metabolites enriched in pregnant women were negatively correlated with pro-inflammatory cytokines, indicating their role in modulating immune responses.
The study also explored associations between gut microbiota, metabolites, and cytokines, suggesting that metabolites may mediate the relationship between microbiota and the immune system. Directional mediation analysis identified specific linkages among microbes, metabolites, and cytokines, indicating the potential influence of certain gut microbes on cytokine levels by modulating metabolite concentrations. For instance, bacteria like Ruminococcus callidus were found to decrease pro-inflammatory cytokines by affecting specific metabolites levels.
The findings provide valuable insights into the complex interplay between gut microbiota, metabolites, and immune function during pregnancy, paving the way for further research and the development of novel therapeutic strategies.