Bacterial information in serum extracellular vesicles reflects the inflammation of adherent perinephric fat

Adipose tissue and bacterial flora are involved in metabolism in the human body. However, the relationship between the two remains unclear. Recently, the presence of circulating bacterial DNAs has been reported. We previously reported the utility of bacterial DNA in serum extracellular vesicles (EVs) for diagnosing patients with renal cell carcinoma (RCC). In this study, we aimed to assess whether there is a correlation between bacterial DNA in serum EVs and inflammation in adipose tissue. We undertook 16S rRNA metagenomic analysis of bacterial DNA in serum EVs from 77 patients with RCC (the derivation cohort). We discovered that DNAs from Enterobacteriaceae, Polaromonas, and Coxiellaceae were highly expressed in patients with low Mayo adhesive probability (MAP) scores. A lower MAP score reflects a reduced risk of dense adipose tissue and adhesions. Additionally, we combined these bacterial DNAs to create the EPC (Enterobacteriaceae, Polaromonas, Coxiellaceae) index that predicts a MAP score of 0. Subsequently, we undertook 16S rRNA metagenomic analysis of bacterial DNA in serum EVs from 32 patients with RCC (the validation cohort). The EPC index could distinguish patients with low MAP scores from those with high MAP scores in the derivation (area under the curve [AUC], 0.76; sensitivity, 56%; specificity, 85%) and validation (AUC, 0.81; sensitivity, 100%; specificity, 62%) cohorts. These results suggest that bacterial DNA in serum EVs could reflect the inflammation of adherent perinephric fat around the kidney.