SGLT2 inhibition does not reduce glucose absorption during experimental peritoneal dialysis

Physiology of peritoneal dialysis; pathophysiology in long-term patients

The microvascular wall of peritoneal tissues is the main barrier in solute and water transport in the initial phase of peritoneal dialysis (PD). Small solute transport is mainly by diffusion through inter-endothelial pores, as is hydrostatic fluid transport with dissolved solutes. Water is also transported through the intra-endothelial water channel aquaporin-1(AQP-1) by a glucose-induced crystalloid osmotic gradient (free water transport). In the current review the physiology of peritoneal transport will be discussed both during the first years of PD and after long-term treatment with emphasis on the peritoneal interstitial tissue and its role in free water transport. Attention will be paid to the role of glucose-induced pseudohypoxia causing both increased expression of fibrogenetic factors and of the glucose transporter GLUT-1. The former leads to peritoneal fibrosis, the latter to a reduced crystalloid osmotic gradient, explaining the decrease in free water transport as a cause of ultrafiltration failure. These phenomena strongly suggest that the extremely high dialysate glucose concentrations are the driving force of both morphologic and functional peritoneal alterations that may develop during long-term PD.

Effects of Sodium-Glucose Cotransporter 2 Inhibitors in Diabetic and Non-Diabetic Patients with Advanced Chronic Kidney Disease in Peritoneal Dialysis on Residual Kidney Function: In Real-World Data

Background and Objectives: Peritoneal dialysis (PD) is a renal replacement therapy modality in which the dialysis dose can be individually adapted according to the patients' residual kidney function (RKF). RKF is a crucial factor for technique and patient survival. Pharmacological strategies aimed at slowing the loss of RKF in patients on PD are limited. Therefore, we aimed to assess the potential effects and safety of sodium-glucose cotransporter 2 (SGLT-2) inhibitors on the preservation of RKF in patients with and without type 2 diabetes mellitus (T2DM) on PD during an average follow-up of 6 months. Materials and Methods: In this retrospective observational, single-center study on real-world data, we included patients from the Peritoneal Dialysis Unit of the Hospital General Universitario de Ciudad Real, who started treatment with SGLT-2 inhibitors during the period from December 2022 to December 2023. Data on analytical and clinical parameters, RKF, and peritoneal membrane transport function were retrospectively collected at months 0, 3, and 6. Results: Out of 31 patients in our unit, 16 prevalent patients initiated treatment with SGLT-2 inhibitors (13 empagliflozin and 3 dapagliflozin). A total of 62.5% were male and the mean age was 67.3 years. The baseline peritoneal ultrafiltration was higher in the non-diabetic patient (NDMP) group than in the diabetic patient (DMP) group. However, the residual diuresis volume, 24 h residual renal clearance rate of urea in urine, and 24 h proteinuria were higher in the DMP group than in the NDMP group. At the sixth month, patients in both groups preserved RKF and diuresis, with a trend towards a non-significant reduction in proteinuria and blood pressure. Only two patients of the DMP group presented adverse effects. Conclusions: The use of SGLT-2 inhibitors in our sample of patients with and without T2DM on PD appears to be safe and effective to preserve RKF.

Effects of sodium-glucose co-transporter 2 inhibitors on ultrafiltration in patients with peritoneal dialysis: a protocol for a randomized, double-blind, placebo-controlled, crossover trial (EMPOWERED)

BACKGROUND

Volume overload is common and associated with high mortality in patients on peritoneal dialysis (PD). Traditional strategies including diuretics, water/salt restriction, and icodextrin-based solutions cannot always fully correct this condition, necessitating novel alternative strategies. Recent studies confirmed the expression of sodium-glucose cotransporter 2 (SGLT2) in the human peritoneum. Experimental data suggest that SGLT2 inhibitors decrease glucose absorption from the PD solution, thereby increasing the ultrafiltration volume. This trial aims to assess whether SGLT2 inhibitors increase the ultrafiltration volume in patients on PD.

METHODS

The EMPOWERED trial (trial registration: jRCTs051230081) is a multicenter, randomized, double-blind, placebo-controlled, crossover trial. Patients with clinically diagnosed chronic heart failure are eligible regardless of the presence of diabetes if they use at least 3 L/day glucose-based PD solutions. Participants will be randomly assigned (1:1) to receive empagliflozin 10 mg once daily and then placebo or vice versa. Each treatment period will last 8 weeks with a 4-week washout period. This study will recruit at least 36 randomized participants. The primary endpoint is the change in the daily ultrafiltration volume from baseline to week 8 in each intervention period. The key secondary endpoints include changes in the biomarkers of drained PD solutions, renal residual function, and anemia-related parameters.

CONCLUSIONS

This trial aims to assess the benefit of SGLT2 inhibitors in fluid management with a novel mechanism of action in patients on PD. It will also provide insights into the effects of SGLT2 inhibitors on solute transport across the peritoneal membrane and residual renal function.

Reporting Practices for Animal Studies on Peritoneal Dialysis Conducted in 2021-2023 after the Introduction of the ARRIVE 2.0 Guidelines

INTRODUCTION

The first version of Animal Research: Reporting of in vivo Experiments (ARRIVE 1.0) guidelines was introduced to improve reporting of animal research but did not lead to major improvements in this respect. This applied also to animal studies on peritoneal dialysis (PD). Here, we examined the performance of the revised version of these guidelines (ARRIVE 2.0).

METHODS

Eighty-nine relevant articles published in 2018-2020 (ARRIVE 1.0 period) and 97 published in 2021-2023 (ARRIVE 2.0 period) were identified in PubMed® and analyzed for completeness and transparency of reporting.

RESULTS

In both periods, most studies were carried out in Asia, on rodents, and concerned the peritoneal pathophysiology. During ARRIVE 2.0, more studies were published in higher impact factor journals with the focus on pharmacology and immunology. Compared to ARRIVE 1.0, general aspects of study design and reporting improved during ARRIVE 2.0 period in studies generated in Europe and USA but did not change significantly in Asia. Detailed analysis showed no global improvement in completeness of reporting key information included in the ARRIVE 2.0 Essential 10 checklist. Articles from both periods were deficient in sample size calculations, use of blinding, recording adverse events and drop-outs, and specification of appropriate statistical methods. The level of reporting during ARRIVE 2.0 did not correspond to the journal impact factor and the presence of recommendations for the use of ARRIVE 2.0 in their instructions to authors.

CONCLUSION

So far, ARRIVE 2.0 has not produced significant improvements in the reporting of animal studies in PD.

The Peritoneal Membrane and Its Role in Peritoneal Dialysis

A healthy and functional peritoneal membrane is key to achieving sufficient ultrafiltration and restoring fluid balance, a major component of high-quality prescription in patients treated with peritoneal dialysis (PD). Variability in membrane function at the start of PD or changes over time on treatment influence dialysis prescription and outcomes, and dysfunction of the peritoneal membrane contributes to fluid overload and associated complications. In this review, we summarize the current knowledge about the structure, function, and pathophysiology of the peritoneal membrane with a focus on clinical implications for patient-centered care. We also discuss the molecular and genetic mechanisms of solute and water transport across the peritoneal membrane, including the role of aquaporin water channels in crystalloid versus colloid osmosis; why and how to assess membrane function using peritoneal equilibration tests; the etiologies of membrane dysfunction and their specific management; and the effect of genetic variation on membrane function and outcomes in patients treated with PD. This review also identifies the gaps in current knowledge and perspectives for future research to improve our understanding of the peritoneal membrane and, ultimately, the care of patients treated with PD.

Quantifying Ultrafiltration in Peritoneal Dialysis Using the Sodium Dip

Key Points

Ultrafiltration (UF) is a key component of clinical peritoneal dialysis prescription, but the traditional method to assess UF is hampered by large inaccuracies. Here we propose a novel method, based on a computational model and on a single dialysate sodium measurement, to accurately estimate UF and osmotic conductance to glucose in patients on peritoneal dialysis.

Background

Volume overload is highly prevalent among patients treated with peritoneal dialysis (PD), contributes to hypertension, and is associated with an increased risk of cardiovascular events and death in this population. As a result, optimizing peritoneal ultrafiltration (UF) is a key component of high-quality dialysis prescription. Osmotic conductance to glucose (OCG) reflects the water transport properties of the peritoneum, but measuring it requires an accurate quantification of UF, which is often difficult to obtain because of variability in catheter patency and peritoneal residual volume.

Methods

In this study, we derived a new mathematical model for estimating UF during PD, on the basis of sodium sieving, using a single measure of dialysate sodium concentration. The model was validated experimentally in a rat model of PD, using dialysis fluid with two different sodium concentrations (125 and 134 mmol/L) and three glucose strengths (1.5%, 2.3%, and 4.25%). Then, the same model was tested in a cohort of PD patients to predict UF.

Results

In experimental and clinical conditions, the sodium-based estimation of UF rate correlated with UF rate measurements on the basis of volumetry and albumin dilution, with a R 2 =0.35 and R 2 =0.76, respectively. UF on the basis of sodium sieving was also successfully used to calculate OCG in the clinical cohort, with a Pearson r of 0.77.

Conclusions

Using the novel mathematical models in this study, the sodium dip can be used to accurately estimate OCG, and therefore, it is a promising measurement method for future clinical use.

Blockade of sodium-glucose co-transporters improves peritoneal ultrafiltration in uraemic rodent models

BACKGROUND

The most used PD fluids contain glucose as a primary osmotic agent. Glucose peritoneal absorption during dwell decreases the osmotic gradient of peritoneal fluids and causes undesirable metabolic consequences. Inhibitors of sodium-glucose co-transporter (SGLT) type 2 are wildly used for the treatment of diabetes, heart and kidney failure. Previous attempts to use SGLT2 blockers in experimental peritoneal dialysis yielded contrasting results. We studied whether peritoneal SGLTs blockade may improve ultrafiltration (UF) via partial inhibition of glucose uptake from dialysis fluids.

METHODS

Kidney failure was induced in mice and rats by bilateral ureteral ligation, and dwell was performed by injection of glucose-containing dialysis fluids. The effect of SGLT inhibitors on glucose absorption during fluid dwell and UF was measured in vivo.

RESULTS

Diffusion of glucose from dialysis fluid into the blood appeared to be sodium-dependent, and blockade of SGLTs by phlorizin and sotagliflozin attenuated blood glucose increment thereby decreasing fluid absorption. Specific SGLT2 inhibitors failed to reduce glucose and fluid absorption from the peritoneal cavity in a rodent kidney failure model.

CONCLUSIONS

Our study suggests that peritoneal non-type 2 SGLTs facilitate glucose diffusion from dialysis solutions, and we propose that limiting glucose reabsorption by specific SGLT inhibitors may emerge as a novel strategy in PD treatment to enhance UF and mitigate the deleterious effects of hyperglycaemia.

Glucose-induced pseudohypoxia and advanced glycosylation end products explain peritoneal damage in long-term peritoneal dialysis

Long-term peritoneal dialysis is associated with the development of peritoneal membrane alterations, both in morphology and function. Impaired ultrafiltration (UF) is the most important functional change, and peritoneal fibrosis is the major morphological alteration. Both are caused by the continuous exposure to dialysis solutions that are different from plasma water with regard to the buffer substance and the extremely high-glucose concentrations. Glucose has been incriminated as the major cause of long-term peritoneal membrane changes, but the precise mechanism has not been identified. We argue that glucose causes the membrane alterations by peritoneal pseudohypoxia and by the formation of advanced glycosylation end products (AGEs). After a summary of UF kinetics including the role of glucose transporters (GLUT), and a discussion on morphologic alterations, relationships between function and morphology and a survey of the pathogenesis of UF failure (UFF), it will be argued that impaired UF is partly caused by a reduction in small pore fluid transport as a consequence of AGE-related vasculopathy and - more importantly - in diminished free water transport due to pseudohypoxia, caused by increased peritoneal cellular expression of GLUT-1. The metabolism of intracellular glucose will be reviewed. This occurs in the glycolysis and in the polyol/sorbitol pathway, the latter is activated in case of a large supply. In both pathways the ratio between the reduced and oxidised form of nicotinamide dinucleotide (NADH/NAD+ ratio) will increase, especially because normal compensatory mechanisms may be impaired, and activate expression of hypoxia-inducible factor-1 (HIF-1). The latter gene activates various profibrotic factors and GLUT-1. Besides replacement of glucose as an osmotic agent, medical treatment/prevention is currently limited to tamoxifen and possibly Renin/angiotensis/aldosteron (RAA) inhibitors.

Current Insights into Cellular Determinants of Peritoneal Fibrosis in Peritoneal Dialysis: A Narrative Review

Peritoneal fibrosis is the final process of progressive changes in the peritoneal membrane due to chronic inflammation and infection. It is one of the main causes of discontinuation of peritoneal dialysis (PD), apart from peritonitis and cardiovascular complications. Over time, morphological changes occur in the peritoneal membranes of patients who use PD. Of those are mesothelial-to-mesenchymal transition (MMT), neoangiogenesis, sub-mesothelial fibrosis, and hyalinizing vasculopathy. Several key molecules are involved in the complex pathophysiology of peritoneal fibrosis, including advanced glycosylation end products (AGEs), transforming growth factor beta (TGF-β), and vascular endothelial growth factor (VEGF). This narrative review will first discuss the physiology of the peritoneum and PD. Next, the multifaceted pathophysiology of peritoneal fibrosis, including the effects of hyperglycemia and diabetes mellitus on the peritoneal membrane, and the promising biomarkers of peritoneal fibrosis will be reviewed. Finally, the current and future management of peritoneal fibrosis will be discussed, including the potential benefits of new-generation glucose-lowering medications to prevent or slow down the progression of peritoneal fibrosis.

Canagliflozin alleviates high glucose-induced peritoneal fibrosis via HIF-1α inhibition

The cardioprotective effects of sodium-glucose cotransporter type 2 (SGLT2) inhibitors have been demonstrated in many studies. However, their benefits for end-stage kidney disease patients, particularly those on peritoneal dialysis, remain unclear. SGLT2 inhibition has shown peritoneal protective effects in some studies, but the mechanisms are still unknown. Herein, we investigated the peritoneal protective mechanisms of Canagliflozin in vitro by simulating hypoxia with CoCl₂ in human peritoneal mesothelial cells (HPMCs) and rats by intraperitoneal injection of 4.25% peritoneal dialysate simulating chronic high glucose exposure. CoCl₂ hypoxic intervention significantly increased HIF-1α abundance in HPMCs, activated TGF-β/p-Smad3 signaling, and promoted the production of fibrotic proteins (Fibronectin, COL1A2, and α-SMA). Meanwhile, Canagliflozin significantly improved the hypoxia of HPMCs, decreased HIF-1α abundance, inhibited TGF-β/p-Smad3 signaling, and decreased the expression of fibrotic proteins. Five-week intraperitoneal injection of 4.25% peritoneal dialysate remarkably increased peritoneal HIF-1α/TGF-β/p-Smad3 signaling and promoted peritoneal fibrosis and peritoneal thickening. At the same time, Canagliflozin significantly inhibited the HIF-1α/TGF-β/p-Smad3 signaling, prevented peritoneal fibrosis and peritoneal thickening, and improved peritoneal transportation and ultrafiltration. High glucose peritoneal dialysate increased the expression of peritoneal GLUT1, GLUT3 and SGLT2, all of which were inhibited by Canagliflozin. In conclusion, we showed that Canagliflozin could improve peritoneal fibrosis and function by ameliorating peritoneal hypoxia and inhibiting the HIF-1α/TGF-β/p-Smad3 signaling pathway, providing theoretical support for the clinical use of SGLT2 inhibitors in patients on peritoneal dialysis.

Narrative Review of glycaemic management in people with diabetes on peritoneal dialysis

There is an increasing number of people with diabetes on peritoneal dialysis (PD) worldwide. However, there is a lack of guidelines and clinical recommendations for managing glucose control in people with diabetes on PD. The aim of this review is to provide a summary of the relevant literature and highlight key clinical considerations with practical aspects in the management of diabetes in people undergoing PD. A formal systematic review was not conducted because of the lack of sufficient and suitable clinical studies. A literature search was performed using PubMed, MEDLINE, Central, Google Scholar and ClinicalTrials.gov., from 1980 through February 2022. The search was limited to publications in English. This narrative review and related guidance have been developed jointly by diabetologists and nephrologists, who reviewed all available current global evidence regarding the management of diabetes in people on PD.We focus on the importance of individualized care for people with diabetes on PD, the burden of hypoglycemia, glycemic variability in the context of PD and treatment choices for optimizing glucose control. In this review, we have summarized the clinical considerations to guide and inform clinicians providing care for people with diabetes on PD.

High versus low ultrafiltration rates during experimental peritoneal dialysis in rats: Acute effects on plasma volume and systemic haemodynamics

INTRODUCTION

Intradialytic hypotension is a common complication of haemodialysis, but uncommon in peritoneal dialysis (PD). This may be due to lower ultrafiltration rates in PD compared to haemodialysis, allowing for sufficient refilling of the blood plasma compartment from the interstitial volume, but the underlying mechanisms are unknown. Here we assessed plasma volume and hemodynamic alterations during experimental PD with high versus low ultrafiltration rates.

METHODS

Experiments were conducted in two groups of healthy Sprague-Dawley rats: one group with a high ultrafiltration rate (N = 7) induced by 8.5% glucose and a low UF group (N = 6; 1.5% glucose), with an initial assessment of the extracellular fluid volume, followed by 30 min PD with plasma volume measurements at baseline, 5, 10, 15 and 30 min. Mean arterial pressure, central venous pressure and heart rate were continuously monitored during the experiment.

RESULTS

No significant changes over time in plasma volume, mean arterial pressure or central venous pressure were detected during the course of the experiments, despite an ultrafiltration (UF) rate of 56 mL/h/kg in the high UF group. In the high UF group, a decrease in extracellular fluid volume of -7 mL (-10.7% (95% confidence interval: -13.8% to -7.6%)) was observed, in line with the average UF volume of 8.0 mL (standard deviation: 0.5 mL).

CONCLUSION

Despite high UF rates, we found that plasma volumes were remarkably preserved in the present experiments, indicating effective refilling of the plasma compartment from interstitial tissues. Further studies should clarify which mechanisms preserve the plasma volume during high UF rates in PD.

Phloretin Improves Ultrafiltration and Reduces Glucose Absorption during Peritoneal Dialysis in Rats

BACKGROUND

Harmful glucose exposure and absorption remain major limitations of peritoneal dialysis (PD). We previously showed that inhibition of sodium glucose cotransporter 2 did not affect glucose transport during PD in rats. However, more recently, we found that phlorizin, a dual blocker of sodium glucose cotransporters 1 and 2, reduces glucose diffusion in PD. Therefore, either inhibiting sodium glucose cotransporter 1 or blocking facilitative glucose channels by phlorizin metabolite phloretin would reduce glucose transport in PD.

METHODS

We tested a selective blocker of sodium glucose cotransporter 1, mizagliflozin, as well as phloretin, a nonselective blocker of facilitative glucose channels, in an anesthetized Sprague-Dawley rat model of PD.

RESULTS

Intraperitoneal phloretin treatment reduced glucose absorption by >30% and resulted in a >50% higher ultrafiltration rate compared with control animals. Sodium removal and sodium clearances were similarly improved, whereas the amount of ultrafiltration per millimole of sodium removed did not differ. Mizagliflozin did not influence glucose transport or osmotic water transport.

CONCLUSIONS

Taken together, our results and previous results indicate that blockers of facilitative glucose channels may be a promising target for reducing glucose absorption and improving ultrafiltration efficiency in PD.

Peritoneal dialysis and peritoneal fibrosis: molecular mechanisms, risk factors and prospects for prevention

Peritoneal dialysis (PD) leads to structural and functional changes in the peritoneal membrane, the endpoint of which is peritoneal fibrosis. Peritoneal fibrosis is diagnosed in 50% and 80% of PD patients within 1 and 2 years of treatment initiation, respectively. A key role in the development of peritoneal fibrosis is played by mesothelial-mesenchymal transformation, a complex biological process of transition from mesothelium to mesenchyme. This review summarizes the current knowledge on the changes in peritoneal function and morphology, the molecular mechanisms of peritoneal fibrosis development, and its clinical consequences during PD. Special attention is given to established and potential risk factors for peritoneal fibrosis, and existing prevention strategies are considered.

The rationale for the need to study sodium-glucose co-transport 2 inhibitor usage in peritoneal dialysis patients

The wave of kidney and heart outcome trials, showing multiple potential benefits for sodium-glucose co-transport 2 (SGLT2) inhibitors, have excluded patients with an estimated glomerular filtration rate below 25 ml/min/1.73 m2. However, dialysis patients are at the highest risk of cardiovascular disease and would benefit most from effective cardioprotective therapies. There is emerging evidence from experimental studies and post hoc analyses of randomised clinical trials that SGLT2 inhibitors are well tolerated and may also be effective in preventing cardiovascular and mortality outcomes in patients with severe chronic kidney disease, including patients receiving dialysis. As such, extending the usage of SGLT2 inhibitors to dialysis patients could provide a major advancement in their care. Peritoneal dialysis (PD) patients have an additional unmet need for effective pharmacotherapy to preserve their residual kidney function (RKF), with its associated mortality benefits, and for treatment options that help reduce the risk of transfer to haemodialysis. Experimental data suggest that SGLT2 inhibitors, via various mechanisms, may preserve RKF and protect the peritoneal membrane. There is sound physiological rationale and an urgent clinical need to execute robust randomised control trials to study the use of SGLT2 inhibitors in PD patients to answer important questions of relevance to patients and healthcare systems.

Aging of the Peritoneal Dialysis Membrane

Long-term peritoneal dialysis as currently performed, causes structural and functional alterations of the peritoneal dialysis membrane. This decay is brought about by the continuous exposure to commercially available glucose-based dialysis solutions. This review summarizes our knowledge on the peritoneum in the initial phase of PD, during the first 2 years and the alterations in function and morphology in long-term PD patients. The pseudohypoxia hypothesis is discussed and how this glucose-induced condition can be used to explain all peritoneal alterations in long-term PD patients. Special attention is paid to the upregulation of hypoxia inducing factor-1 and the subsequent stimulation of the genes coding for glucose transporter-1 (GLUT-1) and the growth factors transforming growth factor-β (TGFβ), vascular endothelial growth factor (VEGF), plasminogen growth factor activator inhibitor-1 (PAI-1) and connective tissue growth factor (CTGF). It is argued that increased pseudohypoxia-induced expression of GLUT-1 in interstitial fibroblasts is the key factor in a vicious circle that augments ultrafiltration failure. The practical use of the protein transcripts of the upregulated growth factors in peritoneal dialysis effluent is considered. The available and developing options for prevention and treatment are examined. It is concluded that low glucose degradation products/neutral pH, bicarbonate buffered solutions with a combination of various osmotic agents all in low concentration, are currently the best achievable options, while other accompanying measures like the use of RAAS inhibitors and tamoxifen may be valuable. Emerging developments include the addition of alanyl glutamine to the dialysis solution and perhaps the use of nicotinamide mononucleotide, available as nutritional supplement.

Dual SGLT1/SGLT2 inhibitor phlorizin reduces glucose transport in experimental peritoneal dialysis

INTRODUCTION

Glucose absorption during peritoneal dialysis (PD) is commonly assumed to occur via paracellular pathways. We recently showed that SGLT2 inhibition did not reduce glucose absorption in experimental PD, but the potential role of glucose transport into cells is still unclear. Here we sought to elucidate the effects of phlorizin, a non-selective competitive inhibitor of sodium glucose co-transporters 1 and 2 (SGLT1 and SGLT2), in an experimental rat model of PD.

METHODS

A 120-min PD dwell was performed in 12 anesthetised Sprague-Dawley rats using 1.5% glucose fluid with a fill volume of 20 mL with (n = 6) or without (n = 6) intraperitoneal phlorizin (50 mg/L). Several parameters for peritoneal water and solute transport were monitored during the treatment.

RESULTS

Phlorizin markedly increased the urinary excretion of glucose, lowered plasma glucose and increased plasma creatinine after PD. Median glucose diffusion capacity at 60 min was significantly lower (p < 0.05) being 196 µL/min (IQR 178-213) for phlorizin-treated animals compared to 238 µL/min (IQR 233-268) in controls. Median fractional dialysate glucose concentration at 60 min (D/D ₀) was significantly higher (p < 0.05) in phlorizin-treated animals being 0.65 (IQR 0.63-0.67) compared to 0.61 (IQR 0.60-0.62) in controls. At 120 min, there was no difference in solute or water transport across the peritoneal membrane.

CONCLUSION

Our findings indicate that a part of glucose absorption during the initial part of the dwell occurs via transport into peritoneal cells.

Acquired Decline in Ultrafiltration in Peritoneal Dialysis: The Role of Glucose

Ultrafiltration is essential in peritoneal dialysis (PD) for maintenance of euvolemia, making ultrafiltration insufficiency-preferably called ultrafiltration failure-an important complication. The mechanisms of ultrafiltration and ultrafiltration failure are more complex than generally assumed, especially after long-term treatment. Initially, ultrafiltration failure is mainly explained by a large number of perfused peritoneal microvessels, leading to a rapid decline of the crystalloid osmotic gradient, thereby decreasing aquaporin-mediated free water transport. The contribution of peritoneal interstitial tissue to ultrafiltration failure is limited during the first few years of PD, but becomes more important in long-term PD due to the development of interstitial fibrosis, which mainly consists of myofibroblasts. A dual hypothesis has been developed to explain why the continuous exposure of peritoneal tissues to the extremely high dialysate glucose concentrations causes progressive ultrafiltration decline. First, glucose absorption causes an increase of the intracellular NADH/NAD⁺ ratio, also called pseudohypoxia. Intracellular hypoxia stimulates myofibroblasts to produce profibrotic and angiogenetic factors, and the glucose transporter GLUT-1. Second, the increased GLUT-1 expression by myofibroblasts increases glucose uptake in these cells, leading to a reduction of the osmotic gradient for ultrafiltration. Reduction of peritoneal glucose exposure to prevent this vicious circle is essential for high-quality, long-term PD.