ESA-SRB-AOTA 2019

Altered gut microbiota composition in early pregnancy in women treated with thyroxine (#524)

Helen L Barrett 1 2 , Leonie K Callaway 3 , H.David McIntyre 2 4 , Marloes Dekker Nitert 5
  1. Mater Research Institute - The University of QLD, Brisbane
  2. Endocrinology, Mater Health, South Brisbane, QLD, Australia
  3. Royal Brisbane and Women's Hospital , Herston, QLD, Australia
  4. Faculty of Medicine, University of Queensland, Herston, QLD, Australia
  5. School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD

Background:

Gut bacteria are known to take up thyroid hormone and could play a role in the recycling of iodothyronines by deconjugating bile-conjugated iodothyronines. Outside pregnancy, hyperthyroidism is associated with altered gut microbiota composition and hypothyroidism with small intestinal bacterial overgrowth. The absorption of orally administered thyroxine therapy is not complete in the small intestine and some thyroxine will reach the gut microbiota in the colon. Thyroxine need increases in pregnancy, likely due to physiological changes, but a significant portion reaches the colon where it could alter the composition of the gut microbiota and alter intraluminal metabolism. Here, we investigated if gut microbiota composition is different in women on thyroxine treatment in early pregnancy.

Methods: Overweight and obese women who participated in the SPRING study and reported using thyroxine were matched with controls not on thyroxine in a 1:2 ratio. Gut microbiota composition at 16 weeks gestation was determined by sequencing the V6-V8 region of the 16S rRNA gene using the QIIME pipeline for analysis. The PiCRuSt was used for predicting the functional capacity of the gut microbiota.

Results: There was no difference in the alpha and beta diversity of the gut microbiota between 8 women on thyroxine and their 16 matched controls at 16 weeks gestation. The gut microbiota of the women on thyroxine showed increased abundance of the genera Bifidobacterium (P=0.045) and Bilophila (P=0.039) but decreased abundance of the Archaea member Methanobrevibacter (P=0.047). Functional prediction analysis indicated increased abundance of bacterial pathways involving DNA replication; DNA repair and recombination; pyrimidine metabolism and amino acid metabolism in women taking thyroxine but lower abundance of the methane metabolism pathway.

Conclusion: These results in a small cohort of overweight and obese pregnant women suggest that thyroxine treatment is associated with altered composition of the gut microbiota in early pregnancy.