The improvement effect of AMS on PF has been proved. Huang et al. (Huang et al., 2003) cultured HMrSV5 cells in vitro and found that a high concentration of AMS not only did not cause cytotoxicity, but also had a significant protective effect in reducing cell destruction, indicating that AMS could reverse the damage caused by high glucose abdominal permeate solution and inflammatory factors, and promote the proliferation of mesothelial cells, with an effect similar to that of steroid drugs. These results suggest that AMS is important for the maintenance of normal peritoneal function. One study randomly assigned 56 patients with continuous ambulatory peritoneal dialysis. By comparing abdominal dialysis before and after treatment, it was found that using abdominal dialysis containing AMS could antagonize the inhibition of abdominal dialysis on macrophage activity and phagocytosis function. At the same time, AMS can increase the secretion of TNF-α and nitrogen oxide, indicating the immune defense function of AMS in PF treatment (M. Zhang et al., 2007). In the process of TGF-β signaling, Smads protein family is a key mediator. When active TGF-β binds to the TGF-β receptor on the surface, it induces phosphorylation of the C-terminal of downstream Smad protein, phospho-Smad2 and Smad3 form heterodimeric complexes with Smad4, and transported to the nucleus (Roberts and Derynck, 2021). High glucose peritoneal dialysis solution can lead to excessive secretion of TGF-β1, and the use of a conventional dose of peritoneal dialysis solution containing AMS injection (10 mg/mL concentration) can reverse the overexpression of TGF-β1, suggesting that AMS plays a certain role in delaying PF through TGF-β (H. Xu et al., 2005). In this process, Smad7 acts as a TGF-β/Smad signaling antagonist to inhibit TGF-β-mediated phosphorylation of Smad2 and Smad3 (Silva et al., 2019). In the rat PF model induced by standard abdominal permeation solution, it was found that AMS injection (contained 2 g/mL crude drug) can alleviate PF, and the mechanism is to inhibit the action of monocyte chemotactic protein-1, thereby reducing the recruitment and activation of monocytes/macrophages. In addition, the expression of TNF-α and TGF-β1 in the peritoneum was reduced after AMS treatment at a dose of 4000 mg/kg, and the reduction of phosphorylated SMAD2/3 also confirmed the inhibitory effect of AMS on TGF-β/Smad pathway (Z. Li et al., 2014), and it was also found that the role of macrophages in peritoneal fibrosis is bidirectional and complex.

The activation marker of the Wnt/β-catenin signaling pathway is the upregulated expression and nuclear translocation of the key protein β-catenin, and Snail is its transcription factor (Schunk et al., 2021). EMT of HMrSV5 cells was induced by TGF-β, and β-catenin and Snail were reduced. After AMS intervention, EMT was further inhibited. The results suggested that AMS could inhibit TGF-β-induced EMT of HMrSV5 cells to a certain extent. Part of the mechanism is through activation of Wnt/β-catenin signaling pathway, inhibition of β-catenin protein expression and inhibition of Snail transcription factor. In addition, Glycogen Synthase Kinase-3 (GSK-3β) can exist in complex form with β-catenin. Some scholars further detected the expression and phosphorylation of GSK-3β and β-catenin proteins in the cytoplasm and nucleus of peritoneal mesodermal cells after AMS intervention, and found that AMS could stabilize GSK-3β and β-catenin complex and degrade β-catenin. The specific mechanism of AMS regulating Wnt/β-catenin signaling pathway was reconfirmed and further discovered (Yu et al., 2018). Wnt/β-catenin signaling pathway can crosstalk with TGF-β signaling pathway (Guo et al., 2017). Based on this, further experiments found that β-catenin can bind to Smad7 protein. It was found that β-catenin may compete with Smad7 after the construction of Smad7 cell lines, and at the same time reduce the inhibitory effect of AMS on EMT to a certain extent, and the same operation was performed in the rat PF model induced by intrapitoneal injection of 4.25% high glucose peritoneal permeate solution, and the results were also similar. It is suggested that AMS can upregulate Smad7 and competitively inhibit β-catenin through both classical Wnt/β-catenin pathway and crosspoilers with TGF-β, and finally reduce β-catenin expression and interfere with PF(Yu et al., 2018). Some studies have found that stimulation of rat peritoneal mesothelial cells with AMS medium can antagonize the upregulation of ROS and NADPH oxidase subunit p47phox expression caused by Angiotensin Ⅱ, and not only reduce ROS production and p47phox expression. It can also inhibit the expression and activity of NADPH oxidase, so it can be inferred that AMS can reduce the production of ROS by inhibiting the activity of NADPH oxidase, thus blocking its signal transduction, inhibiting the overexpression of TGF-β1 downstream, reducing the occurrence of EMT, and delaying PF (J. Xu et al., 2010). In addition, the experiments of Liu et al. (X. Liu et al., 2014) showed that TGF-β significantly induced the expression of NADPH oxidase subunit p67phoxmRNA and protein in rat peritoneal mesothelial cells, and induced intracellular ROS production, which could be significantly improved by AMS stimulation.

In conclusion, a certain concentration of AMS not only does not cause damage to the body, but also has a protective effect on PF, which is specifically reflected in the fact that AMS can act on the target of TGF-β, interfere with EMT through the associated cytokine network, and improve the oxidative stress in the body to balance the production of ROS, Further, regulate the downstream TGF-β related signaling pathway. However, the research direction of AMS is too simple and not deep enough, only stays in the upstream medium. At the same time, for other cytokines, such as connective tissue growth factor and other downstream mediators, these studies are not clear. Therefore, the mechanism of AMS regulating PF still needs to be further studied (Figure 2).

AS-IV, isoastragalus Ⅰ, acetoflavin Ⅰ, Fusarium flavin A, Fusarium flavin B and soybean saponin Ⅰ were isolated from Astragalus memeranaceus. In TGF-β-induced EMT models, AS-IV decreased the expression of vimentin and phospho-Smad2/3 in a dose-dependent manner and increased the expression of Smad7. Therefore, it is speculated that AS-IV can alleviate PF by up-regulating Smad7 in TGF-β/Smad signaling pathway (Z. Li et al., 2013). In addition to the classical Smad pathway, TGF-β can also promote cell survival, proliferation, and collagen synthesis by activating the PI3K/Akt pathway (Y. E. Zhang, 2009). Yu et al. found that TGF-β1 upregulates β-catenin when inducing EMT in HMrSV5 cells, while AS-IV can degrade β-catenin to a certain extent. β-catenin is not only involved in stabilizing cell adhesion, but also a key signaling molecule in the Wnt signaling pathway. At the same time, AS-IV can inhibit the high expression of p-Akt, p-GSK-3β and p-mTOR. Compared with Akt inhibitor MK226, mTOR inhibitor rapamycin and Akt pathway agonist Insulin, it is found that AS-IV is likely to delay PF through the AKt pathway (Yu et al., 2019).

NLRP3 receptor protein 3 inflammasome (NLRP3 inflammasome) is a multiprotein complex, located in the cytoplasm and is named by NOD-like receptor protein 3 (NOD-like receptorprotein 3, NLRP3 inflammasome). NLRP3, apoptosis-associated speck-like potein containing a CARD, and cysteinyl aspartate specific proteinase-1 (Caspase-1), and the activation of NLRP3 inflammasome on the one hand will lead to the release of pro-inflammatory mediators such as interleukin1-β (IL-1β) and interleukin-18, this can induce the progression of inflammation (Lamouille et al., 2014), on the other hand, also can induce the scorch death of damaged cells (J. Chen and Chen, 2018). Zhang et al. (L. Zhang et al., 2015) found that high-glucose peritoneal dialysis solution could activate NLRP3 inflammasome-related parts in a time-dose-dependent manner, such as NLRP3, pro-caspase-1 precursor containing cysteine, IL-1β precursor and IL-1β. AS-IV can partially inhibit peritoneal mesothelial-to-mesenchymal transition by blocking its activation in a concentration-dependent manner. At the same time, the inhibition of the NLRP3 inflamome by AS-IV is not the same as the complete block of other small molecule compounds (such as dopamine receptor-1), but is more likely to partially restore the homeostasis of the low level of NLRP3 activation.

By establishing an in vitro HPMCs/HMrSV5 cell model, Li et al. (Z. Li et al., 2019) confirmed that AS-IV can reduce mitochondrial membrane lipid peroxidation caused by high glucose dialysis solution by reducing the production of ROS, thus alleviating the disorder of charge distribution inside and outside mitochondria, protecting mitochondrial function, improving oxidative stress, and ultimately inhibiting apoptosis induced by mitochondrial damage. On the other hand, AS-IV can control the expression of the translocator of the outer mitochondrial membrane (Tom), although it has no significant effect on the expression of Tom20. However, Tom70 can be upregulated to reverse the damage caused by high glucose dialysate and protect the mitochondrial translocase system. It has also been observed that AS-IV could reduce the expression levels of dynamin related protein-1 and recombinant human mitochondrial fission protein. It also promoted the expression of optic atrophy rotein, a mitochondrial fusion protein. Therefore, it is speculated that AS-IV can improve HPMCs injury and protect peritoneal structure and function through the above pathways. In addition, experiments have shown that ROS may act AS a second messenger to regulate the Smads signaling pathway and mediate the occurrence of EMT, and AS-IV can reduce the production of ROS to inhibit the phosphorylation of Smad2/3, thus achieving the purpose of inhibiting and reverting EMT, similar to the ROS scavenger n-acetylcysteine (NAC) (Shi et al., 2016).

Ferroptosis is a cell death mode different from apoptosis, necrosis, and autophagy, and its main feature is induced lipid peroxidation (Stockwell et al., 2017). Cao Huimin et al. (Cao et al., 2021) found that there was iron death in the HMrSV5 model, and AS-IV could protect cells by inhibiting iron death. In this study, it was found that after the intervention of AS-IV, the level of Fe²⁺ and ROS decreased, the content of MDA decreased, and the content of GSH increased. The expression of cell tumor antigen p53 and Acyl-CoA synthetase long-chain family member 4 was downregulated. The expression of solute carrier family 7 member 11 (SLC7A11,xCT)and glutathione peroxidase 4 (GPX4) was upregulated. It is suggested that AS-IV may protect peritoneal cells by reducing Fe2+ content, inhibiting ROS production and enhancing xCT and GPX4 activity through cystine/glutamate reverse transporter (xCT)/GPX4 pathway.

Proliferator-activated receptor coactivator-1α (PGC-1α) is an important transcription coactivator of cell kernel receptors. Its primary function is to regulate the synthesis of mitochondrial proteins, including subunits of the respiratory chain complex, by activating nucleus respiratory factor 1 (NRF-1). In addition, PGC-1α binds to transcription factor mitochondrial A, TFAM, thereby initiating the replication and transcription of mitochondrial DNA (Feng et al., 2016). Some studies (Z.-H. Li et al., 2022) suggested that the expression of Bcl-2 in rat stromal cells with fibrosis induced by high glucose was inhibited, and similar changes were also observed in the expression of PGC-1α, NRF-1 and TFAM. However, after Astragalus total saponins (ATS) treatment, the expression of these proteins increased, and after interfering with PGC-1α treatment, the expression of ATS on cell viability and mitochondrial number, including related proteins, showed a downward trend. Therefore, it is speculated that the intervention mechanism of ATS is to promote the expression of PGC-1α and increase mitochondrial synthesis, thereby inhibiting apoptosis and fibrosis-related proteins. Reduce fiber collagen synthesis and fiber tissue proliferation, thereby reducing the degree of PF (Figure 3).

In conclusion, Astragalus saponins (including AS-IV), AS-IV, the main active ingredient of AMS, can delay fibrosis by regulating oxidative stress, apoptosis and inhibiting inflammatory response.

It has been shown that high glucose peritoneal permeate decreases the mitochondrial membrane potential of HMrSV5, and APS can reverse this process. In addition, APS can also downregulate the protein expression of Bcl-2-associated X protein and cleaved Caspase3 and upregulate Bcl-2, antagonizing cell apoptosis and protecting peritoneal tissue, and it is confirmed that APS is associated with the expression level of proteins related to mitochondrial apoptosis of HMrSV5 (Zhao, Shan, et al., 2020). Vascular endothelial growth factor (VEGF) can induce endothelial cell proliferation and promote angiogenesis. Appropriate angiogenesis can promote tissue repair, but when the degree of angiogenesis exceeds a certain limit, the peritoneal glucose absorption rate will increase, resulting in the disappearance of peritoneal osmotic concentration gradient and the reduction of peritoneal ultrafiltration. On this basis, some scholars have found that APS can inhibit the expression of VEGF protein level, thereby inhibiting angiogenesis and reversing the occurrence of fibroperitoneal maintenance in PD rats (Feng et al. , 2024) In conclusion, APS protects peritoneal tissue mainly by regulating mitochondria-related proteins and VEGF. Recently, it has been reported in the literature that APS can inhibit the TLR4/NF-κB signalling pathway and reduce apoptosis, thus ameliorating the occurrence of idiopathic pulmonary fibrosis in mice. Surprisingly, the authors also found that the gut microbiota can also affect lung disease through the gut-lung axis, and APS can increase the proportion of intestinal probiotics, reduce harmful bacteria, and balance the gut microbiota by regulating the metabolic pathway, which ultimately leads to therapeutic effects. This exists as an inspiration for us to study the treatment of PF (Wei et al., 2023).