Fibroblast activation is a normal component of wound healing; however, in PD patients, it becomes persistent and leads to the accumulation of activated myofibroblasts that alters the healthy structure and function of the peritoneal membrane, thus hindering the effective treatment (Strippoli et al., 2020; Pap et al., 2020). EMT, a complex biological process in the peritoneal membrane, involves the transformation of PMCs which lose epithelial phenotype (apical, basal polarity) and detach from characteristic basement membrane/ECM attachment, and acquire myofibroblast-like cells characteristics such as invasive ability and mesenchymal phenotype (Figure 2) (Wilson et al., 2020; Yáñez-Mó et al., 2003).

Cellular trans-differentiation is a complex phenomenon that converts epithelial cells into mesenchymal cells. This biological process, called EMT, depends on the extracellular environment rather than the genome (Stone et al., 2016). EMT results in the loss of cell polarity and junctions and the gain of fibroblastic shape and invasiveness (Figure 3) (Stone et al., 2016). EMT occurs in both physiological (e.g., organogenesis, development, wound healing, and regeneration) and pathological (e.g., fibrosis, metastasis) conditions (Leggett et al., 2021). PMCs migrate and proliferate on the serosal lining (Tsai et al., 2018) and differentiate into myo-fibroblasts (EMT), which may promote fibrotic conversion (Sandoval et al., 2016) Changes in the gene expression and phenotype of PMCs, making them deposit more collagens and fibronectin and increasing their motility, which facilitate the development of peritoneal fibrosis (Strippoli et al., 2016).

EMT may play a pivotal role in the early decline of UF capacity, which constitutes the most critical functional impairment during the initial years of PD. A significant correlation has been established between UF efficiency and the dialysate-to-plasma (D/P) creatinine ratio, indicating a shared pathophysiological mechanism (Krediet, 2024; Davies, 2004). However, in many cases, the degree of UF impairment exceeds what would be anticipated based solely on D/P creatinine values (Krediet, 2024). This paradox—characterized by increased solute transport (elevated D/P creatinine) alongside diminished UF—is a hallmark of UF failure secondary to peritoneal fibrosis (Del Peso et al., 2008). The net consequence is fluid overload in PD patients, despite apparent solute equilibration, underscoring the dissociation between solute and water transport in the fibrotic peritoneal membrane.

In addition, during EMT, changes in cell membrane receptors, signaling molecules such as TGF-β1, Src, Hypoxia-inducible factor (HIF-1α), and cell morphology and behavior occurs (Wilson et al., 2020). EMT involves complex pathological cross-talk among PMCs, endothelial cells, immune cells, and resident fibroblasts (Strippoli et al., 2020). TGF-β1, is constitutively expressed by the PMCs and plays a major role in the maintenance of a transformed, inflammatory micro-environment in peritoneal membrane (Wilson, 2018). It enhances HIF-1α expression, which drives cell growth, extracellular matrix production and cell migration (Wilson, 2018). Importance of pro-fibrotic, TGF-β1 signalling during EMT of PMCs has been demonstrated by using TGF-β receptor inhibitor GW788388 on the EMT signalling pathway (Lho et al., 2021). Therapeutic Interventions targeting EMT process are detailed in Table 1.

Mechanotransduction, the process of transforming mechanical signals into biochemical events, along with extracellular biochemical factors, regulates various cellular functions and is crucial during development, physiological and pathological conditions (Terri et al., 2021; Strippoli et al., 2020; Orr et al., 2006; Santos and Lagares, 2018). Biomechanical alterations of the ECM, including increased ECM rigidity or forces of varying strengths and dynamic characteristics, modulate form and the functions of cells with an inevitable impact on the cellular behavior and therefore drive distinct fibrotic signaling pathways (Orr et al., 2006; Santos and Lagares, 2018; Chen, 2008). PD requires the infusion of large amounts of PD solutions into the peritoneal cavity, which exposes the peritoneal membrane to biomechanical forces. These forces include mechanical stretch of PMCs and augment intra-abdominal pressure. Additionally, reports state that abdominal surgeries can drive fibrotic conversion pertaining to the vast majority of adhesion myofibroblasts which arise from surface mesothelium followed by EMT process which may induce biomechanical injury to the peritoneal membrane leading to peritoneal adhesions formation (Sandoval et al., 2016; Zindel et al., 2021). Proliferation and migration of mesothelial cells is promoted by receptor tyrosine kinases of the ERBB family, Epidermal Growth Factor Receptor (EGFR), which is documented to be involved in post-surgical peritoneal adhesions (Zindel et al., 2021). Mechanical injury and hypoxia identified by injured surface mesothelium expressing podoplanin (PDPN)/mesothelin (MSLN) and upregulation of hypoxia-inducible factor 1 alpha (HIF1α) are involved in the fibrotic process and the development of peritoneal adhesions suggested in an in vivo study (Tsai et al., 2018).

Peritoneal fibrosis, which is caused by inflammation, infection, or long-lasting dialysis, leads many patients to discontinue PD, however, its mechanism is unclear. Epigenetic shifts are involved in peritoneal fibrosis, and emerging evidence indicates that epigenetic interventions could help ward off and treat peritoneal fibrosis in practice (Tsai et al., 2018; Wang et al., 2021). Epigenetic regulation in peritoneal fibrosis is complicated, mainly affecting the changes of signalling molecules, transcriptional factors, and genes (Tsai et al., 2018; Wang et al., 2021). The primary epigenetic transformations include, changes in the expression and activity of genes (such as DNA methylation, histone modifications), and different types of non-coding RNA molecules (such as microRNAs (miRNAs), long non-coding RNAs, and circular RNAs) can also play a role in the development of peritoneal fibrosis (Tsai et al., 2018; Sandoval et al., 2016; Wang et al., 2021; Guo et al., 2020). HDAC inhibitors are discussed in Table 1 and 2. The development of peritoneal fibrosis (PF) is significantly influenced by non-coding RNAs, particularly microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). miRNAs are known to regulate key molecular pathways involved in PF and are increasingly being recognized as potential diagnostic biomarkers and therapeutic targets (Sandoval et al., 2016; Guo et al., 2020; Huang et al., 2023). For instance, miR-15a-5p is found to be downregulated in long-term PD patients, suggesting a role in fibrosis progression. Beyond this, a range of other miRNAs—including miR-199a-5p, miR-214-3p, miR-153-3p, miR-129-5p, miR-21, miR-30a, miR-145, miR-30b, miR-200, miR-302c, miR-34a, and miR-29b—have been reported to interact with hypoxia-inducible factor-1α (HIF-1α), a key regulator in fibrotic signaling (Sandoval et al., 2016; Guo et al., 2020). Concurrently, growing evidence suggests that lncRNAs also contribute to the pathogenesis of peritoneal fibrosis, although their precise mechanisms remain under investigation. As research in this field advances, it is crucial to identify practical approaches for targeting these non-coding RNAs to improve peritoneal fibrosis diagnosis and treatment.

Recent study gives a rational basis and underscores the likely role of gut microbiota dysbiosis in peritoneal fibrosis (Lho et al., 2021; Stepanova, 2023). Compared to healthy controls, PD patients had less Actinobacteria and Firmicutes in their faecal microbiota, with a notable decrease in Bifidobacterium and Lactobacillus, and more Pseudomonas aeruginosa, according to a study by Wang et al. (2012). By lowering the pH through the production of acetic acid and lactic acid, Bifidobacterium and Lactobacillus influence the host positively, either by preventing the growth of pathogenic bacteria or by competing with them for nutrients and adhesion sites (Wang et al., 2012). ESRD induced alterations in the gut microbiota compromise the intestinal barrier and facilitate the translocation of microbial components and endotoxins into the systemic circulation and peritoneal cavity. Dorea, Clostridium, and SMB53 are related to chronic low-grade inflammation, oxidative stress, and immune responses within and beyond the peritoneum, peritonitis in ESRD patients on PD (Wang et al., 2012; Stadlbauer et al., 2017; Luo et al., 2021).

A study revealed, in PD patients, uremic toxins such as indoxyl sulfate (IS) and p-cresol sulfate (PCS) accumulate due to increased gut permeability and incomplete clearance and increase the host’s susceptibility to pathogen invasion. This, along with catheter use and dietary restrictions, disrupts the intestinal microenvironment, promoting pathogenic bacteria and reducing beneficial short chain fatty acids (SCFAs)-producing microbes. Consequently, PD patients exhibit a higher relative abundance of Proteobacteria in their gut microbiota (Simões-Silva et al., 2018). Proteobacteria, a potential marker of gut dysbiosis, shows similar abundance in PD patients and their healthy family members. This suggests that long-term hospitalization, rather than dialysis alone, may contribute to gut microbiome alterations in PD patients (Teixeira et al., 2023).

In PD patients, gut microbiota differs in both taxonomic composition and metabolic function. Those with longer dialysis duration, higher peritoneal glucose exposure, and reduced residual renal function show distinct microbiome profiles and significantly lower fecal levels of SCFAs, including isobutyric and isovaleric acids (Jiang et al., 2021). Identifying these alterations can provide valuable insights for clinicians, enabling early and targeted interventions to reduce complications and mortality risk in patients with ESRD. A study documented, patients on PD had more pathogenic and less beneficial species in their faecal microbiome, which altered the predicted metagenome functions, compared to controls (Stadlbauer et al., 2017).

In recent years, Probiotics, prebiotics, and synbiotics have been reported to reduce uremic toxins such as endotoxins and p-cresol in PD patients. These interventions may also lower mortality rates associated with long-term PD. Additionally, they have been shown to improve gastrointestinal symptoms and enhance the quality of life in PD patients (Li et al., 2025).

Probiotic capsules containing Bifidobacterium longum, Lactobacillus bulgaricus, and Streptococcus thermophilus have been shown to enhance gastrointestinal absorption and digestion (Li et al., 2025). They also help reduce inflammatory markers, such as C-reactive protein (CRP) and Interleukin-6 (IL-6) (Pan et al., 2021). Elevated IL-6 levels in PD patients are associated with malnutrition and altered peritoneal small solute transport rates, which can increase mortality. A randomized controlled trial (RCT) noted that PD patients improved serum indoxyl sulfate (IS) levels by consuming 21 g/day of unripe banana flour. Insulin-type fructan decreases Bacteroides thetaiotaomicron, the IS-producing bacterium, by inhibiting its tryptophanase activity. This leads to reduced IS production in the gut of these patients (de Andrade et al., 2021). In severe cases of uremic toxicity related to p-cresol or para-cresol sulfates, synbiotics can promote the growth of Bifidobacterium bifidum strains and increase Lactobacillus abundance in the gut. This intervention effectively reduces intestinal p-cresol levels (Stuivenberg et al., 2022). Although clinical research on gut microbiomes in PD patients remains limited in scale, further studies may validate the use of probiotics, prebiotics, and synbiotics. These interventions have the potential to improve the gut microbiome and reduce complication rates in PD.

Chronic Peritoneal inflammation is considered as an important event during the pathogenesis of PF (Zhang et al., 2017). Peritoneal injury leads to the activation of signal transducer and activator of transcription 3 (STAT3) and nuclear factor kappa-B (NF-κB), which also promotes the release of multiple proinflammatory cytokines/chemokines (Shi et al., 2021). Peritoneal mesothelium-derived CXC chemokine ligand 1 (CXCL1), a chemokine, associates with peritoneal micro vessel density in uremic patients undergoing PD. Thus, CXCL1 and its receptors may be novel targets for therapeutic intervention to prolong PD therapy (Catar et al., 2022). Other pharmacological interventions targeting receptors involved in inflammation in the peritoneal membrane dysfunction culminating to fibrosis are detailed in Table 2.

A major factor limiting the chronic use of PD remains peritoneal membrane failure due to prolonged exposure to bioincompatible PD solutions leading to the fibrosis of the membrane (Cho et al., 2014). Recent evidences have tried to explain the mechanisms linking inflammation–either infection-induced (peritonitis) or sterile (bioincompatible PD solutions) – involved with the cellular stress and membrane injury in the pathogenesis and regulation of PD related peritoneal fibrosis (Zhou et al., 2016; Honda and Oda, 2005; Fielding et al., 2014; Raby et al., 2017).

The peritoneal cavity has a normal environment that can be disturbed by bio incompatible PD solutions, which can also harm the peritoneal membrane. Traditional (Bio-incompatible) PD solutions have non-physiological features such as low pH (acidic), high lactate and glucose concentrations (hyperglycaemic) (1.5%–4.5%) (Mortier et al., 2002), and hyperosmotic dextrose solutions to achieve a sufficient UF gradient across the peritoneal membrane, and toxin elimination by maintaining electrolyte homoeostasis (Szeto and Johnson, 2017; McIntyre, 2007). However, they also trigger fibrosis, oxidative stress and microinflammation in the peritoneum, leading to changes in its structure and function which involves PMCs depletion and basement membrane breakdown leading to ultrafiltration failure, discontinuation of PD, and an increased risk of developing EPS (Terri et al., 2021; Jagirdar et al., 2019; Kang, 2020). Furthermore, heat sterilisation of PD solutions results in glucose instability generating toxic glucose degradation products (GDPs), glyoxal, 3,4-dideoxyglucosone-3-ene, methylglyoxal (MGO), and others (Jörres, 2012; Catalan et al., 2005). MGO is an extremely toxic GDPs that causes oxidative stress and peritoneal injury as well as reported to enhance the production of vascular endothelial growth factor (VEGF), which may lead to vascular permeability (Hishida et al., 2019). Furthermore, many GDPs such as 3,4-dideoxyglucosone-3-ene (3,4-DGE) are reactive carbonyl compounds which along with glucose form advanced glycation end-products (AGEs), binds to free amino groups on membrane proteins or lipids contributing to pathophysiological alterations in the peritoneal membrane (Linden et al., 2002; Mortier et al., 2004). Bio-incompatible PD solutions recruit immune cells such as Th17, gdT cells, and neutrophils to the sub-mesothelial zone, where they produce inflammatory cytokine, IL-17A.

Most important, the role of IL-17A in peritoneal membrane injury and other PD-related complications has been recently explored (Marchant et al., 2020). This cytokine activates the NF-κB pathway in PMCs, which drives the expression of factors such as IL-6 which then activates the JAK/STAT pathway promoting EMT in PMCs (Marchant et al., 2020).

During peritoneal membrane injury in PD, IL-17A production in the local site stimulates the release of more pro-inflammatory mediators, such as cytokines and chemokines, from infiltrating cells and resident peritoneal cells. This amplifies the inflammatory response promoting fibrosis and angiogenesis in the peritoneal membrane (Marchant et al., 2020).

Oxidative and cellular stress plays a key role in the peritoneal membrane damage. Free radicals in the PD effluent indicate a higher risk of technique failure in stable patients (Morinaga et al., 2012; Xu et al., 2015). Hypertonic PD solutions with high glucose and/or low pH induces oxidative stress and cause apoptosis and autophagy PMCs (Simon et al., 2017; Hara et al., 2017; Wu et al., 2018). Peritoneal membrane damage further involves mitochondrial mechanisms (Ramil-Gómez et al., 2021) pertaining to the Reactive Oxygen Species (ROS) production (López-Armada et al., 2013). In a study the authors measured mitochondrial reactive oxygen species (mtROS) and membrane potential in PMCs with different phenotypes. They found that fibroblast-like PMCs had more mtROS and less membrane potential than epithelial-like PMCs. They also demonstrated that mtROS induced EMT in omental MCs, which was prevented by mitoTEMPO. Moreover, they showed that mitochondrial DNA (mtDNA) levels in PMCs correlated positively with dialysate/plasma creatinine ratio (D/P Creat) and negatively with UF (Ramil-Gómez et al., 2021; López-Armada et al., 2013).

These results suggest that mitochondrial dysfunction drives EMT in PMCs leading to peritoneal membrane damage. Furthermore, pertaining to cellular stress and membrane damage, mitochondria release damage-associated molecular patterns (DAMPs-mtROS or mtDNA), recognized by the innate immune system, and thus triggering pro-inflammatory and pro-fibrotic responses by activating Toll-like receptors (TLRs), and purinergic receptors (Raby et al., 2018; Mills et al., 2017; Anders and Schaefer, 2014). Raby et al. conducted a study to evaluate the involvement of TLRs and DAMPs in PD solutions-induced membrane fibrosis. They exposed human uremic peritoneal leukocytes, PMCs and mouse peritoneal leukocytes to different PD solutions (bio-incompatible or more bio-compatible) for a prolonged period and measured the pro-inflammatory DAMPs, measured fibrotic responses at the mRNA/protein levels and assessed the role of TLR2/4 in the sterile peritoneal inflammation and fibrosis (Raby et al., 2018). A study has shown that Nucleotide-binding oligomerization domain-like receptor (NLR) family pyrin domain containing 3 (NLRP3) inflammasome, a member of the NLR family of intracellular sensors, also mediates sterile inflammation by regulating the release of the pro-inflammatory cytokine IL-1β which promotes peritoneal membrane damage and fibrosis (Hishida et al., 2019). Pharmacological Interventions targeting oxidative stress and their products are detailed in Table 2.

New PD solutions that are more bio-compatible have been made to mitigate the problem. Newer PD solutions, such as icodextrin, and taurin solutions, have been designed to reduce the deleterious effects of bio incompatible PD solutions exposure on the peritoneal membrane (del et al., 2016; Santamaría et al., 2015), and they help to sustain the physiological equilibrium of the peritoneal cavity. Icodextrin, is gradually absorbed from the peritoneal cavity which facilitates a sustained colloid osmotic gradient, resulting in enhanced UF compared to conventional PD solutions. Owing to its superior fluid removal capacity and reduced systemic glucose exposure, icodextrin is particularly advantageous for long-dwell PD exchanges in patients with high peritoneal solute transport rates, where it aids in optimizing volume status while minimizing the metabolic burden associated with glucose absorption (Dousdampanis et al., 2018; Ng et al., 2022). Biocompatible PD solutions, expose the patients to less Glucose Degradation Products (GDPs) than conventional solutions, and better preserve the residual renal function and diuresis with a decrease in peritonitis frequency, are created by using the following approaches: pH adjustment to neutral and GDP minimisation; bicarbonate (±lactate) buffering; glucose polymer substitution for dextrose (which also reduces pH along with GDP); and amino acids as osmotic agents (Htay et al., 2018; Zhou et al., 2016; Yohanna et al., 2015) (Table 3). Recent evidence suggests, sodium-glucose cotransporters (SGLTs) and glucose transporters (GLUTs) in the peritoneal membrane mediate glucose handling and absorption during glucose-based PD (Balzer et al., 2020).

PD solutions act as double edge sword for peritoneal membrane. Biocompatible solutions for PD have some advantages over conventional bio-incompatible solutions, but they also have some drawbacks (Table 4). One of the main challenges is their higher cost in some countries, which may limit their accessibility and affordability. Another issue is the lack of clear evidence on how they affect patient-level clinical outcomes, such as survival and quality of life. Therefore, their role in clinical practice needs to be further defined and evaluated.

Peritonitis, a significant side effect, leads to PMCs damage, fibrosis, morbidity, and technical failure (Chou et al., 2022; Perl et al., 2020). Pro-fibrotic growth factors such as TGF-β1 and Fibroblast Growth Factor-2 (FGF-2) and inflammatory cytokines like IL-1β, IL-6, and others are upregulated during peritonitis (Kawaguchi et al., 2000; Virzì et al., 2022). IL-1β expression possibly relates inflammation and peritonitis intimately to the beginning and maintenance phase of the peritoneal fibrosis (Honda and Oda, 2005; Helmke et al., 2019). Likewise, IL-6 has been well connected to inflammation for functioning as solute transport increase across the PM (Wilson, 2018; Yang et al., 2020). Macrophages are reported to be the most abundant cells in PD effluent, which defines a central role in chronic inflammation (Helmke et al., 2019; Yang et al., 2020).

CX3CR1, receptor of CX3CL1 (detected on the peritoneal mesothelium), is expressed on macrophages in the peritoneal membrane (Helmke et al., 2019). A report demonstrated, dialysate exposure induces peritoneal fibrosis through CX3CR1-CX3CL1-mediated macrophage-mesothelial communication, which could be a novel therapeutic strategy for peritoneal fibrosis (Helmke et al., 2019). Based on the current data, peritonitis-induced membrane injury is associated with reduced membrane Cregs and altered complement activation products, such as C and C5b-9. The study also compared peritoneal injuries caused by fungal and P. aeruginosa peritonitis with those caused by Gram-positive bacterial peritonitis. Severe peritoneal membrane injuries due to fungal and P. aeruginosa peritonitis could result in the loss of expression of CRegs in the peritoneum, which increases deposition of complement activation products, suggesting deleterious effects in the membrane and further impaired Creg expression (Fukui et al., 2023). Zindel et al. documented, bacterial contamination activates mesothelial EGFR signalling in postsurgical PF, leading to MC-derived myofibroblasts and peritoneal adhesion (Zindel et al., 2021). Moreover, the authors in a 20-year PD cohort examined the peritoneal membrane characteristics and found that the high peritoneal transport group had a higher risk of peritonitis than the low or intermediate transport groups, even after adjusting for demographics, comorbidities, and biochemical parameters (Chou et al., 2022).

Peritoneal membrane solute transport and angiogenesis are regulated by matrix metalloproteinase 9 (MMP9) via β-catenin signaling. These factors impair ultrafiltration, cause chronic hypervolemia, and increase the risk of technique failure and mortality in PD patients (Padwal et al., 2017). Authors report that MMP9 mRNA expression in PMCs from peritoneal effluent of PD patients correlates with membrane solute transport properties and suggeste suggestes a role for MMP9 in peritoneal membrane injury. They proposed that MMP9 induced peritoneal angiogenesis by cleaving E-cadherin and activating b-catenin signaling, which increased VEGF expression (Padwal et al., 2017). New blood vessels form through angiogenesis, a highly complex process that depends on the balance between growth factors that stimulate or inhibit it (Zhu et al., 2021). Peritoneal angiogenesis plays a key role in developing peritoneal fibrosis (Zhu et al., 2021). Studies showed that TGF-β1 and VEGF-A mediate fibrosis in PD patients (Kinashi et al., 2018; Kariya et al., 2018). TGF-β1 stimulates VEGF-A expression, which in turn promotes angiogenesis (Kinashi et al., 2018; Kariya et al., 2018), indicating that the TGF-β1-VEGF-A pathway plays a key role in fibrosis-associated peritoneal angiogenesis (Kariya et al., 2018).

Twist, a basic helix-loop-helix DNA-binding protein, regulates E-cadherin expression and induces EMT and MMP9 expression in PMCs. The study revealed that peritoneal membrane injury increased Twist expression in the peritoneum (Margetts, 2012).

In a uremic rodent model, angiogenesis and fibrosis have been demonstrated during PD, accompanied by increased expression of angiopoietin (Ang)-2 and reduced expression of Ang receptor Tie2 (Stone et al., 2016; Yuan et al., 2009). With bio-incompatible PD solutions, AGEs and IL-6 can promote the production of VEGF, which has been detected in the effluent of long-term PD patients and involved in inflammation (Stone et al., 2016; Yuan et al., 2009). Therapeutic interventions targeting angiogenesis in the peritoneum are detailed in (Table 2).

The main signaling pathways responsible for the EMT process in PMCs are induced by TGF-β1 (Davies, 2004). Heterodimeric serine/threonine kinase transmembrane receptor complexes mediate the signaling of TGF-β1 factors. The ligand binds to its primary receptor (receptor type II), which recruits, trans-phosphorylates, and activates the signaling receptor (receptor type I). The receptor type I of TGF-β1, also known as activin receptor-like kinase 5 (ALK5), phosphorylates Smad2 and 3 with its serine-threonine kinase activity. BMP-7 (ALK3) receptor type I phosphorylates Smads (1, 5, and 8). The phosphorylated Smads form heterodimers with Smad4, a common mediator of all Smad pathways (Gangji et al., 2009; Xu et al., 2009; Loureiro et al., 2011). These Smad heterocomplexes move to the nucleus, binding directly to DNA and activating specific target genes. Inhibitory Smad seven limits the Smad signaling triggered by TGF-β1. They prevent the phosphorylation and/or nuclear translocation of Smad2/3 or Smad1/5/8complexes and induce their degradation by recruiting ubiquitin ligases (Gangji et al., 2009; Suryantoro et al., 2023) MMT process arises from the integration of diverse signals triggered by multiple factors, making it difficult to establish a clear hierarchy or prioritize specific pathways (López-Cabrera, 2014).

The contribution of TGF-β1-BMP7-Gremlin-1-Smad pathway cross-talk has recently been reported to be involved in peritoneal fibrosis (Ruiqi et al., 2021). The authors report a possible mechanism, Gremlin-1 enhances the TGF-β1 signalling and suppresses the expression of BMP7 and Smad1/5/8, leading to EMT and peritoneal fibrosis (Ruiqi et al., 2021). In other study, BMP-7 inhibitory effect on EMT is dependent on the activation of Smad1/5/8 proteins that counteract TGF-β1 activated Smad2/3 activity (Raby et al., 2018). Smad3 signalling is essential for TGF-β1 induced EMT and fibrosis, as evidenced by Smad3 knockout mice. These mice display less peritoneal fibrosis, collagen accumulation, and EMT (Patel et al., 2010). EMT and peritoneal membrane fibrotic injury are reduced by inhibitory Smad7, which blocks Smad signaling (Patel et al., 2010).

Documentation of TGF-β1/Smads signaling help in understanding the fibrosis mechanism partially, but still, the entire phenomenon is incompletely understood. Complementing, the Smad proteins crosstalk with various non-canonical pathways to communicate downstream responses. Non-canonical pathways such as Mitogen activated protein kinases (MAPKs), Extracellular regulated Kinases (ERK1/2), and p-38, along with Jun N-terminal kinases (JNK), Src, phosphatidyl inositol 3 kinase (PI3Kinase)/AKT, Wnt/β-catenin/Ror2 signalling pathways, and NLRP3 inflammasome transduce the pro-fibrotic effects of TGF-β1 concluding to EMT and fibrosis as discussed below.

Map kinase (MEK)-ERK1/2 is a key pathway that mediates the effects of TGF-β1 on EMT and fibrosis (Gui et al., 2012). However, ERK- nuclear factor κ-light chain-enhancer of activated B cells (NF-kB)-Snail-1 pathway inhibition prevents this EMT induction. Moreover, the pathway inhibition also triggers mesenchymal to epithelial transition (MET), reverse process of EMT, in PMCs of patients on long term PD (Strippoli et al., 2008). The AMPK-NF-kB pathway mediates the anti-fibrotic molecule mechanism, which suppresses suppressing PAI-1 expression in PMCs and prevents TGF-β1 induced EMT in peritoneal fibrosis. (Strippoli et al., 2008).

In continuation of non-Smad pathways, TGF-β1 is reported to activate TAK-1 (TGF-β activated kinase 1), which mediates the phosphorylation and activation of p38 and JNK MAPKs pathway (Shim et al., 2005). The p38-mediated pathway controls the EMT process of PMCs through a feedback mechanism that reduces ERK1/2, TAK-1-NF-κB activities. JNK inhibition is stated to preserve E-cadherin expression and prevents EMT conversion (Strippoli et al., 2010). JLP, a (JNK interacting protein) family scaffold protein for MAPK pathway (Dhanasekaran et al., 2007), negatively regulates peritoneal fibrosis by modulating TGF-β1/Smad signalling pathway, EMT, autophagy, and apoptosis (Tian et al., 2022).

PI3K/AKT pathway is another non-Smad mechanism that has been widely investigated in EMT process, contributes pathologically to fibrosis (Lamouille et al., 2014). A report indicated that blocking the PI3K/AKT/mTOR pathway enhanced autophagy and reduced PF during PD (Jia et al., 2022). By reducing intracellular ROS levels, this inhibition enhances the expression of ZO-1 and E-cadherin, and suppresses the expression of p-PI3K/PI3K, p-mTOR/mTOR, fibroblast-specific proteins ferroptosis suppressor protein 1 (FSP1), and α-SMA, which are associated with fibroblast differentiation, thus alleviating fibrosis (Suryantoro et al., 2023). The PI3K/AKT pathway also plays a role in EMT. Wang et al. found that AKT is overactivated during MMT (Jia et al., 2022), and the expression levels of p-AKT and α-SMA in PMCs are significantly inhibited after intervention with the PI3K/AKT pathway blocker wortmannin (Jia et al., 2022). A recent study showed that rat PMCS incorporated adipose-derived mesenchymal stem cell-derived extracellular vesicles (ADSC-EVs) and exhibited increased proliferation and migration via the activation of MAPK-ERK1/2 and PI3K-Akt pathways, which prevented postoperative peritoneal adhesions (Shi M. et al., 2022).

Src activation contributes to peritoneal fibrosis by stimulating the TGF-β1 pathway in a chlorhexidine-stimulated model of peritoneal membrane injury (Wang et al., 2017). Src is required for the phosphorylation of TGF-β receptor (R)-II, which activates TGF-β1. TGF-β1 plays a critical role in EMT programming via Smad and non-Smad RAS/RAF/MEK/ERK pathways; the PI3K/AKT/mTOR pathway; and the STAT3 pathway, which regulate the expression of SNAIL, c-Myc and Cyclin D1 (Wilson et al., 2020).

When peritoneal injury and oxidative stress occurs in PMCs, nuclear high mobility group box 1 (HMGB1) protein, a DAMP, leaks out of the cells. This activates NF-κB, a transcription factor that regulates inflammatory responses. The recognition of HMGB1 by pattern recognition receptors (PRRs) such as Toll-like receptors (TLRs), nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs), and receptors for advanced glycation end-products (RAGE), receptors for both DAMPs and pathogen-associated molecular patterns (PAMPs), mediates this activation (Wilson et al., 2020; Liu et al., 2017). DAMPS or PAMPS activate PRRs (Raby and Labéta, 2018), which trigger inflammatory and proliferative events through NF-κB, cytokine and TGF-β1 release and IRAK signaling (IRAK) (Balzer, 2020; Raby and Labéta, 2018). These events activate EMT transcription factors SNAIL, TWIST, and ZEB, repress E-cadherin expression, and induce EMT (Wilson et al., 2020).

PMCs express TLRs such as TLR1, 2 and 5 excluding TLR4, which play an important role in the membrane inflammation process (Colmont et al., 2011). Various cell types, including peritoneal leukocytes and PMCs, express TLRs-2 and 4 in particular, which are major receptors for DAMPs (Raby et al., 2017; Anders and Schaefer, 2014; Colmont et al., 2011). TLRs recognise and respond to a wide range of DAMPs, such as HMGB-1 and HSPs (Anders and Schaefer, 2014; Chen and Nuñez, 2010). TLRs trigger MyD88 dependent signalling pathway upon ligand binding, leading to the activation of ERK1/2, JNK, p38 MAPKs, and NF-kB, as well as the secretion of proinflammatory cytokines, such as IL-6, IL-1β and TNF-α (Colmont et al., 2011). IL-1β induces NF-κB response more strongly than TGF-β1 in PMCs, and their co-stimulation results in an additive effect. NF-κB inhibition prevents EMT induction by TGF-β1/IL-1β costimulation and partially reverses EMT in PMCs obtained from PD patients (Strippoli et al., 2008).

Vascular endothelial growth factor (VEGF) is a specific mitogen of vascular endothelial cells (Lamouille et al., 2014). VEGF belongs to a gene family that includes VEGFA, placental growth factor, VEGFB, C, and D. IL-6, IL-1β, IL-8, MCP-1, TNF-α, and Prostaglandin E2, all involved in angiogenesis, endothelial cells survival, proliferation and capillary tube formation (Colmont et al., 2011). Inhibiting VEGF expression could reduce pathological angiogenesis in the membrane of the long-term PD patients, a report documents (Colmont et al., 2011) Another study documents, inhibiting VEGF attenuates fibrosis, by regulating TGF-β1 expression through the phosphoinositide 3-kinase (PI3K)/Akt pathway (Lee et al., 2008). Peritoneal tissues of PD patients with PF express VEGF significantly more than those of PD patients without PF (Abrahams et al., 2014). Peritoneal fibrosis, involves angiogenesis of human peritoneal vascular endothelial cells (HPVECs) mediated by VEGF/VEGF receptor 2 (VEGFR2) signalling. This signalling pathway also interacts with Hippo/YAP signalling, which regulates cell proliferation and differentiation. Pharmacological inhibition of VEGF/Hippo/YAP signaling reduced peritoneal angiogenesis and prevented further damage to the peritoneal membrane (Zhu et al., 2021). High glucose activates estrogen receptor 1 (ESR1) in PMCs, which induces EMT and peritoneal fibrosis in long term PD. ESR1 transcriptionally regulates H19, a long non-coding RNA that interacts with the transcriptional coactivator p300 to enhance the expression of VEGFA. Targeting the ESR1/H19/VEGFA pathway pharmacologically can attenuate high glucose-induced peritoneal fibrosis (Zhao et al., 2023).

PM inflammation and fibrosis are associated with the activation of NLRP3 inflammasome, an intracellular complex of the innate immune system. It activates caspase-1 and controls the secretion of cytokines IL-18 and IL-1β in response to PD solutions with high glucose content (Hishida et al., 2019).

The wingless-type mouse mammary tumor virus integration site family (WNT) signalling pathway has two branches: the canonical branch, which depends on β-catenin, and the non-canonical branch, which does not. The canonical WNT signalling pathway interacts with the TGF-β1 pathway and enhances fibrosis in various organs (He et al., 2009; Guo et al., 2012). Wnt/β-catenin signaling pathway is involved in the EMT of PMCs (Fan et al., 2021). WNT5A is a typical example of a non-canonical WNT protein (Mikels et al., 2009).

A fibrosis marker that can be accessed in the dialysate would help us identify PD patients with peritoneal membrane deterioration and high risk of complications (Li YC. et al., 2021).

IL-6, a chronic peritoneal inflammation marker, is the main biomarker used in PD and measured in dialysis fluid (Suryantoro et al., 2023; Li YC. et al., 2021). Bacterial clearance and infection (acute or subclinical) in PD patients can be assessed by IL-6 levels in PD effluent. Certain biomarkers present in dialysis fluid, such as IL-6, IL-8, and cancer antigen-125 (CA-125), are employed to estimate the quantity of peritoneal macrophages (PMCs) and assess the overall health of the peritoneal membrane (Masola et al., 2022). Some are emerging, like inflammatory markers (Th17 secreted IL-17, T reg cells, and M1/M2 macrophages), some are excreted by PMCs such as miRNAs, aquaporin-1 (AQP-1) (Lopes Barreto and Krediet, 2013) and also markers of cell stress/ageing/senescence, advanced oxidized protein products (AOPPs) (Corciulo et al., 2019). The European Training and Research in PD Network (EuTRiPD) network covers them all (Aufricht et al., 2017). Furthermore, one study provides evidence for the role of AQP-1 as the ultrafiltration mediator in the human peritoneal membrane (Corciulo et al., 2019). Tweaking of Th17 response and boosting the Treg response, might save the peritoneal membrane from damage as explicated in the study (Corciulo et al., 2019). Exposure to hyperglycemic dialysate induces oxidative stress-mediated cellular senescence. Therefore, dialysate advanced oxidized protein products levels may reflect PMC senescence and injury. Moreover, dialysate toxicity and inflammation followed by MMT process modulate the expression of Hsp27 and Hsp72. Dialysate levels of VEGF, MMP-2, and Plasminogen activator inhibitor-1 (PAI-1), associated with PD duration, may serve as indicators of PD-linked peritoneal fibrosis, according to prospective cohort studies (Corciulo et al., 2019). Proteomics and metabolomics could find new biomarkers in PD effluent that could signal PM problems. The metabolic state in PD effluent could tell how healthy the membrane is and how long it will survive. Metabolic profiling of serum and PD effluent may facilitate the evaluation of PM permeability and the early detection of PM dysfunction. Furthermore, metabolite-enriched PD solutions may prevent membrane inflammation and fibrosis, thereby preserving the peritoneal membrane’s permeability (Devuyst et al., 1998). One study suggested that effluent decoy receptor-2 (eDcR2) levels may reflect peritoneal fibrosis in PD patients (Kondou et al., 2022). Moreover, serum α-Klotho and galectin-3 levels were associated with peritoneal membrane thickness and PD duration (Yang et al., 2022). A study has shown that increased dialysate-to-plasma (D/P) creatinine ratio is associated with increased risk of mortality in PD patients (Padwal et al., 2018). The same study has demonstrated that the WNT1 gene and protein expression are correlated with peritoneal solute transport rate (PSTR) measured by D/P creatinine. Therefore, WNT1 may be a biomarker for clinical outcomes in PD patients (Padwal et al., 2018). Osteopontin, a phosphorylated glycoprotein involved in inflammation, EMT, and fibrosis may also be a useful indicator of peritoneal deterioration in long term PD patients (Li J. et al., 2021). Regression analysis of 109 PD patients showed Osteopontin levels in peritoneal effluents were an independent predictive factor for the increased PSTR (Li J. et al., 2021; Kothari et al., 2016) Effluent dialysate mtDNA levels could serve as a prognostic biomarker of peritoneal membrane damage induced by PD (Ramil-Gómez et al., 2021; Xie et al., 2019). High CCL8 levels in PD effluents may be associated with an increased risk of PD failure, and the CCL8 pathway is associated with PF (Lee et al., 2023). A study, using Fourier transform infrared (FTIR) spectroscopy, characterized the molecular profiles of PD effluents and clinical data, and used machine learning to assess the potential of this proof-of-principle study for low-cost, high-speed diagnosis in PD (Grunert et al., 2020). A recent study, highlighting that MMT associated biomarkers and clinical data under Machine Learning models (MAUXI software) can predict endurance and different PD technique failures, opening new avenues to individual treatments (Arriero-País et al., 2025). List of Markers are detailed in Table 5.