Gut microbiota-derived metabolite trimethylamine N-oxide as a biomarker in early Parkinson's disease

Objectives: This study aimed to investigate the potential of using changes in the plasma levels of trimethylamine N-oxide (TMAO), a gut microbiota-derived metabolite, as a biomarker in early Parkinson's disease (PD). Methods: Plasma TMAO levels were measured in 85 patients with drug-naïve early stage PD and 20 healthy controls. A linear mixed model was used to assess longitudinal changes in levodopa-equivalent dose (LED) during follow-up (>2 y) in three tertile PD groups according to plasma TMAO levels. Additionally, a Cox regression analysis was performed to assess the effect of plasma TMAO levels on dementia conversion. Results: Plasma TMAO levels of patients with PD were lower than those of healthy controls. A linear mixed model demonstrated that patients with PD and lower levels of TMAO (<4.75 μmol/L; i.e., lowest tertile group) exhibited faster increases in LED over time. The Cox regression model did not reveal that plasma TMAO level was associated with the risk for dementia conversion (P = 0.488). However, when we divided patients with PD into two subgroups according to bet cutoff TMAO level to maximize the log-rank statistics, the PD group with a low plasma TMAO level (<6.92 μmol/L) had a higher risk (with borderline statistical significance) for PD–dementia conversion than the group with a high TMAO level (hazard ratio: 7.565; 95% confidence interval, 1.004−57.019; P = 0.050). Conclusions: The results demonstrate that lower baseline plasma TMAO levels are associated with faster increases in LED and tend to increase the risk for PD–dementia conversion, suggesting the prognostic implications of TMAO in early stage PD.