NEW INSIGHTS ON TMAU MECHANISMS: UNVEILING A NEW ROLE OF FMO3 HAPLOTYPES AND A POSSIBLE MICROBIOTA CROSSTALK WITH NERVOUS SYSTEM

Trimethylaminuria is a rare metabolic syndrome characterized by excessive excretion of trimethylamine (TMA) from body fluids. The latter is a malodorous amine, synthesized by specific gut bacterial families, that causes the typical rotten fish odor in affected patients. The primary form (TMAU1) is determined by causative mutations in FMO3 gene inherited in an autosomal recessive pattern. It encodes for the enzyme Flavin monooxygenase 3 that converts TMA to odorless TMA-N-oxide (TMAO). The secondary form is linked to environmental factors, especially gut dysbiosis. To date, several aspects of both forms are unclear, so the diagnosis is often uncertain, and it is difficult to advise the correct therapeutic approach to the patient. One of the objectives of the present work was to investigate the role of some haplotypes on the FMO3 enzyme catalytic activity. To do this, a TMAO/TMA urine quantification by 1H-NMR spectroscopy was performed in 38 suspected TMAU patients. Subsequently, a mutational analysis was realized by Sanger sequencing. Detected variants were in silico characterized by a docking prediction for TMA/FMO3 and an unbinding pathway study were performed. Furthermore, the gut microbiota 16s rRNA sequencing of 12 patients, negative to FMO3 screening, was performed to verify a possible dysbiosis condition. In addition, a metabolic pathways analysis was performed to clarify the possible network between bacterial metabolites and behavioral disturbances, phenotype common to many TMAU patients. The results obtained showed that the FMO3 haplotypes could modify the enzyme catalytic activity probably by reducing the interaction time between the FMO3 catalytic site and the TMA or by compromising the TMA N-oxidation process. Analysis of bacterial metabolite pathways has shown that there is a connection between TMA production, metabolites (short-chain fatty acids and neurotransmitters) and psychiatric disorders. The mental disturbs affecting TMAU patients are probably not only related to social consequence of their metabolic disease but also to a physiopathological effect determined by TMA accumulation. These studies, if confirmed with in vitro and in vivo experiments, could improve the TMAU diagnosis.