Investigation of the intestinal microbiota in Meniere's disease
MÃ©niÃ¨re's disease (MD) is an intractable disorder characterized by paroxysms of intense rotatory vertigo and auditory symptoms such as aural fullness and hearing loss. Although there is known to be endolymphatic hydrops involved in the pathological process, the pathogenesis of the disease is still largely unclear. MD is frequently comorbid with obesity, arthritis, chronic fatigue syndrome, hay fever, rhinitis, eczema, drug allergy, irritable bowel syndrome, gastro-esophageal reflux disease, migraine, and psoriasis. Approximately half of patients with MD suffer from depressive symptoms and high levels of several stress hormones were observed in MD and depression, simultaneously. Recently, gut microbes have been shown to influence the function of central nervous system in humans through their metabolites. The relationship between MD and intestinal microbiota still remains unknown. Thus, studying the intestinal microbiota in patients with MD could lead to understand the pathogenesis of MD and develop a new therapeutic approach. The study goals are to investigate and determine if changes in the intestinal microbiota affect the inner ear function of MD patients. We studied the intestinal microbiota of 10 patients with MD and 11 healthy donors (HD). The participants collected fecal samples during a period without any abdominal discomfort. DNA extraction from the fecal samples was performed using an automated DNA extraction machine. The V1-V2 region of the 16S rRNA gene was amplified using a forward primer with the KAPA HiFi Hot Start Ready Mix. To sequence the 16S amplicons using the Illumina MiSeq platform, dual index adapters were attached using the Nextera XT Index kit. Library preparations were performed according to the Illumina 16S library preparation protocol. Libraries were sequenced using the MiSeq Reagent Kit v2 and 250-bp paired ends. The paired-end reads of the partial 16S rRNA gene sequences were analyzed using QIIME2 . Taxonomic information was assigned to each ASV by using a naive Bayes classifier in the QIIME 2 classifier with the 16S gene of the V1-V2 region data of SILVA  to determine the identity and composition of the bacterial genera. We obtained alpha diversity index scores, such as observed operational taxonomic unit numbers, Shannon index scores, and Faith PD scores, in HD and MD. We compared clinical parameters, such as age, disease duration, dizziness handicap inventory scores, and BMI, and laboratory parameters, such as audiometry results and alpha diversity index scores between HD and MD. Significant negative correlations were found between disease duration and alpha diversity indexes of gut microbes in patients with MD. Relative abundance of the species Butyricicoccus ambiguous taxa was increased in patients with MD compared with that of HD. In contrast, Oscillospiraceae UCG-002/UCG-005 ambiguous taxa and Anaerovoracaceae (Eubacterium) brachy group uncultured bacterium were increased in the relative abundance of HD than that of patients with MD. Relative abundance of the Butyricicoccus species was positively correlated with disease duration. Thus, these compositional alterations of gut microbes in patients with MD are associated with inner ear pathologies, such as endolymphatic hydrops, by changing the metabolite profiles in the intestine.The datasets generated during the current study are available in the DDBJ repository, accession number BioProject: PRJDB17474