Association of Enterococcus faecalis and tyrosine decarboxylase gene levels with levodopa pharmacokinetics in Parkinson’s disease

Multiple factors affect the absorption of orally administered levodopa, the gold standard for the treatment of Parkinson's disease (PD). Enterococcus faecalis (E. faecalis) expresses the enzyme tyrosine decarboxylase (tyrDC), which metabolizes levodopa into dopamine and thereby may influence its absorption in patients with PD. This study investigated the association between fecal E. faecalis and tyrDC gene levels and the pharmacokinetics of orally administered levodopa in 21 patients with PD. Our results revealed a significant association between elevated fecal levels of E. faecalis and tyrDC gene levels and reduced peak plasma levodopa concentrations. Additionally, among patients receiving levodopa-carbidopa intestinal gel treatment, strong positive correlations were observed between E. faecalis and tyrDC gene levels in fecal samples and those from the tip of the jejunal tube. Further prospective studies are required to explore the potential role of gut microbiota as a therapeutic target in patients with PD.