Bo-Ning Cao ¹ Cai-Yan Zhang ^2* Zhen Wang ^1* Yao-Xian Wang ^1,3*

• ¹ Dongzhimen Hospital, Beijing University of Chinese Medicine, Beijing, China
• ² 中国人民解放军总医院, 北京市, China
• ³ 河南中医药大学, 河南省, China

To investigate the causal relationship between microbiota, diabetic nephropathy, and blood metabolites through a randomized Mendelian study.In this study, we used 412 microbiota as exposures, 1,400 blood metabolites as intermediaries, and diabetic nephropathy as the outcome. We conducted a two-way Mendelian randomization (MR) analysis to explore the causal relationship between microbiota and diabetic nephropathy, followed by mediation analyses and two-step MR to identify potential blood metabolites.Results: There is a causal relationship between microbiota and diabetic nephropathy. Specific bacteria and metabolites, such as Escherichia coli str. K-12 substr. MG1655, Listeria monocytogenes 10403S, g_Adlercreutzia, g_Haemophilus, g_Bacteroides, Escherichia coli CFT073, and metabolites like Pyrraline, Glycocholenate sulfate, alpha-ketoglutarate, tetradecadienoate (14:2), Cys-gly oxidized, Methylsuccinate, and various others, were identified. Escherichia coli str. K-12 substr. MG1655 is positively related to alpha-ketoglutarate levels, while alpha-ketoglutarate levels and Sphingomyelin (d18:1/18:1, d18:2/18:0) are negatively related. The bacterial microbiota involved in fatty acid oxidation is associated with diabetic kidney disease (DKD) progression, positively correlated with glycocholenate sulfate levels, and negatively correlated with the phosphate linoleyl-tetraenyl-glycerol (18:2 to 20:4) ratio.Additionally, Listeria monocytogenes 10403S is positively correlated with N -acetyl-isoputreanine and negatively correlated with X-12462. Anaerobic ferment ation-related bacteria were positively related to N-acetylcarnitine, 5-acetylamino-6-formyluracil, and negatively correlated with 5-acetamino-6-amino-3-methyluraci l (X-24243). Escherichia coli CFT073 was positively associated with X-16580.Interactions between Bacillus species and metabolites such as d18:1/18:1, d18:2/ 18:0, 2-aminophenol sulfate, and cholate were negative when compared to tetra decadienoate (14:2). g_Adlercreutzia is positively correlated with N-delta-acetylo rnithine, methylsuccinate, and N-acetyl-isoputreanine but negatively correlated w ith N-acetylglucosamine and N-acetylgalactosamine. g_Haemophilus was positive ly associated with arachidoylcarnitine but negatively correlated with X-24531. T he results were heterogeneous and multi-efficacious.For the first time, MR analysis provides supportive evidence for a bidirectional causal relationship between microbiota and diabetic nephropathy and identifies specific genes associated with the disease. The results suggest that probiotic therapy may play a significant role in preventing diabetic nephropathy and improving the quality of life and survival rates of affected patients. Furthermore, this study provides additional evidence of a causal relationship between specific microbiota, diabetic nephropathy, and blood metabolites.