Ramulus Mori (Sangzhi) Alkaloids Improve Pancreatic β-Cell Function Through Gut Microbial and Intra-Islet 2-Methoxyestradiol Biosynthesis

Background: Ramulus Mori (Sangzhi) Alkaloids (SZ-A) are natural hypoglycemic compounds known to enhance insulin secretion. Given the emerging role of the gut microbiota in regulating β-cell function, in this study, we aimed to investigate whether SZ-A exert their beneficial effects through modulating the gut microbiota and its metabolites. Methods: A diabetic mouse model was established using a high-fat diet and streptozotocin, followed by 20 weeks of SZ-A treatment. Gut microbiota and metabolites were profiled via 16S rRNA sequencing and liquid chromatography–mass spectrometry, respectively. Spearman’s correlation analysis was used to explore associations between gut microbiota and metabolites. Single-cell RNA sequencing (scRNA-seq) was used to assess gene expression and signaling pathway changes in β cells. Results: Our results demonstrate that SZ-A alleviated hyperglycemia and increased islet numbers in T2DM mice. SZ-A treatment also reshaped the gut microbiota, notably enriching quantities of Lactobacillus and norank_f__Eubacterium_coprostanoligenes_group, which may contribute to increasing levels of 2-methoxyestradiol (2-ME), a bioactive metabolite. Moreover, scRNA-seq revealed an increased proportion of COMT+ cells in the islets, suggesting that 2-ME may also be synthesized within the islets. In vitro, 2-ME suppressed HIF-1α signaling and promoted insulin secretion, indicating that 2-ME may act as a crucial mediator of the beneficial effects of SZ-A. Conclusions: SZ-A improve β-cell function by increasing 2-ME levels via gut microbiota modulation and islet production, ultimately suppressing HIF-1α signaling and restoring β-cell homeostasis.