Introduction
Human health has always been a concern; this is particularly the case as rates of incidence of various diseases and metabolic disorders increase. Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease featuring hyperglycemia and is generally accompanied by dysfunctions of fat, protein, and carbohydrate metabolism. The diabetic population is expected to grow from 578.4 million in 2030 to 700.2 million by 2045, 90% of which are due to T2DM. T2DM has substantially threatened global human health ( DeFronzo et al., 2015 ; Jiang et al., 2022 ; Que et al., 2021 ).

Evidence shows the involvement of intestinal microbiota of human in lots of health conditions and diseases ( Chen et al., 2021 ). The gastrointestinal tract is a complex ecosystem comprising over 1,000 distinct species of microbiota. Changes within this ecosystem, including shifts in microbial community composition, increases in pathogenic microorganisms and alterations in microbial metabolite profiles, can disrupt host homeostasis. Such disruptions may contribute to the development of various diseases ( Chen et al., 2024 ). T2DM was the first disease reported in association with gut microbiota in 2010 ( Larsen et al., 2010 ). Existing research into T2DM onset and progression has identified intestinal floral imbalance as a critical factor for T2DM patients, their gut microbiota contained rich gram-negative bacteria, particularly those in phyla Bacteroidetes and Proteobacteria ( Dash et al., 2023 ). Outer membranes of these bacteria contain lipopolysaccharide (LPS) that may cause metabolic endotoxemia, which has a meaningful relation to macrophage-elements, oxidative stress, and setup inflammatory cytokines that induce insulin resistance (IR) ( Cunningham, Stephens & Harris, 2021 ). Thus, implementation of targeted interventions on the intestinal microbiota can efficiently reshape the equilibrium of the gut microbiotal structure and function, as well as its metabolites. These interventions can also modulate the multifaceted interactions between the intestinal barrier and the microbiota, resulting in a significant improvement in T2DM ( Chen et al., 2024 ). Additionally, the enhancement of insulin sensitivity through changing the composition of gut microbiota has attracted interest among numerous researchers. This finding indicates that targeted interventions designed to modulate the gut microbiota could serve as a potentially effective strategy for managing T2DM ( Liu et al., 2022a ).

Currently, T2DM drugs mainly include sulfonylureas, biguanides, peroxisome proliferator-activated receptor-γ (PPARγ) agonists, α-glucosidase inhibitors, incretin mimetics, and SGLT2 inhibitors ( Padhi, Nayak & Behera, 2020 ; Sairam et al., 2024 ). Sulfonylureas enhance the release of insulin from pancreatic islets; biguanides decrease the production of hepatic glucose; PPARγ agonists enhance insulin action; α-glucosidase inhibitors interfere with glucose absorption in gut. The primary mechanism of incretin mimetics is to modulate the incretin system. They bind to and activate glucagon-like peptide-1 (GLP-1) receptors located on pancreatic β-cells, thereby triggering insulin synthesis and secretion. SGLT2 inhibitors promote glycosuria by suppressing the reabsorption of glucose in the kidneys ( Hansen, Vilsbøll & Knop, 2010 ). At therapeutic doses, the SGLT2 inhibitors lead to the excretion of approximately 60–100 g of glucose, which directly reduces glucose levels in systemic circulation and contributes to lowering the level of blood glucose ( Brown et al., 2021 ). Nevertheless, their efficacy is far from satisfactory owing to drug resistance, their high price, and side effects, including severe hypoglycemia, low therapeutic efficacy caused by ineffective or improper dosage regimens, weight gain, low potency, and changed adverse effects because of lack of target specificity and drug metabolism, and problems pertaining to permeability and solubility ( Han et al., 2022 ; Sairam et al., 2024 ; Wang et al., 2016 ). To address these problems, many efforts have been made to find natural products that are efficient in alleviating T2DM with no severe adverse effects ( Fei et al., 2024 ). To prevent and treat hyperglycemia, researchers have focused increasing efforts on the discovery of active components in medicinal plants, particularly from traditional Chinese medicines (TCM) ( Wang et al., 2023 ). Polysaccharides from natural sources, as macromolecular carbohydrates, cannot be digested and absorbed in human intestine, so they can reach the colon to promote growth of selective probiotics. They show a beneficial effect on the metabolism of glycolipid. Active polysaccharides, as a natural microecological regulator for intestine, have been extensively used to regulate intestinal tumors, microecology, and inflammation considering the stable efficacy, rich availability, and slight side effects ( Fang et al., 2019 ). Previous research proved that polysaccharides derived from plants are regulatory factors beneficial for intestinal flora disorder in T2DM patients ( Kakar et al., 2021 ; Liu et al., 2024b ; Wu et al., 2019c ).

Scrophularia ningpoensis Hemsl is a famed popular TCM and health food commonly known as Xuanshen. It contains abundant nutrients, like alkaloids, amino acids, and flavonoids, particularly carbohydrates, which are key effective agents in S. ningpoensis ( Gong et al., 2020 ; Hua, Qi & Yu, 2014 ). Prior research has found that the aqueous extract of S. ningpoensis reduces fasting blood glucose level and increases the insulin content in T2DM rats ( Lu et al., 2017 ). This extract improves insulin sensitivity by modulating the AMP-activated protein kinase (AMPK)-mediated suppression of the NLRP3 inflammasome and alleviates pancreatic β-cell pyroptosis via AMPK-dependent inhibition of NLRP3/GSDMD activation ( Yan et al., 2022 ). Polysaccharides derived from S. ningpoensis exhibit hypoglycemic properties, enhancig carbohydrate and fat metabolism, increasing insulin levels, and significantly reducing blood glucose. They also inhibit the overproduction of inflammatory cytokines and modulate the MAPK pathway, including ERK, JNK and p38 proteins ( Ma et al., 2019 ; Ren et al., 2021 ). Many polysaccharides, serving as macromolecular prebiotics, have been shown to promote the proliferation of intestinal probiotics and improve host metabolic functions ( Wang et al., 2016 ). However, limited research is available on the influences of SNP on gut microbiota composition and metabolism in T2DM patients. In-vitro models provide the advantage of reducing influences from the complex in-vivo environment ( Wu et al., 2023 ). An in-vitro anaerobic fermentation model of SNP was established by taking fresh feces of eight T2DM patients and eight healthy humans to explore how SNP affects gas production and microbial communities in the intestine. Besides, variations of gut microbial metabolites and intestinal microbiota were jointly explored using a metabolomic method. The present research estimated the effect of SNP treatment upon T2DM and studied the underlying mechanisms in which intestinal flora and metabolites are involved, offering experimental data for developing SNP healthcare drugs or products to prevent and treat T2DM.