A genome-wide association study suggests correlations of common genetic variants with peritoneal solute transfer rates in patients with kidney failure receiving peritoneal dialysis

Recent advances in the understanding of the peritoneal membrane

PURPOSE OF REVIEW

The efficiency of peritoneal dialysis (PD) as a life-sustaining replacement therapy for patients with kidney failure relies on the integrity and function of the peritoneal membrane. Here, we review the most recent advances in the understanding of the peritoneal membrane and its role in PD.

RECENT FINDINGS

A recent update of the ISPD guidelines proposed a revised definition of membrane dysfunction, emphasizing the importance of fluid balance in patients treated with PD and identified three main mechanisms leading to insufficient peritoneal ultrafiltration (UF). The Bio-PD study, the first genomewide association study in PD, demonstrated that 20% of the interindividual variability in the peritoneal solute transfer rate is genetically determined, and identified several loci of potential relevance for peritoneal transport. A candidate-gene approach identified and characterized a common and functional variant in the promoter of the AQP1 gene associated with water transport and clinical outcomes in PD. Innovative strategies to preserve the integrity of the peritoneal membrane and to enhance UF are also discussed, including the use of gliflozins; steady glucose concentration PD; modulation of GLUT proteins; and cytoprotective additives.

SUMMARY

A comprehensive understanding of the peritoneal membrane and of the mechanisms driving UF may help individualizing PD prescription and improving outcomes in patients treated with PD.

Aquaporin-1 and Osmosis: From Physiology to Precision in Peritoneal Dialysis

The discovery of the aquaporin family of water channels has provided a molecular counterpart to the movement of water across biological membranes. The distribution of aquaporins in specific cell types, their selectivity and very high capacity for water permeation, and the control of their expression and/or trafficking are key to sustain osmosis in multiple tissues. Here, we review the convergent evidence demonstrating that aquaporin-1 (AQP1) facilitates water transport across endothelial cells in the peritoneal membrane, a key process for peritoneal dialysis-the leading modality of home-based dialysis therapy for patients with kidney failure. Genetic and pharmacologic studies in mouse and cell models indicated that AQP1 plays a critical role in crystalloid osmosis, with clinically relevant effects on water transport and risk of death and technique failure for patients on dialysis. By contrast, AQP1 plays no role in colloid osmosis. These studies substantiate potential strategies to improve free water transport and ultrafiltration in patients treated by peritoneal dialysis.

Exploring the impact and utility of genomic sequencing in established CKD

Clinical genetics is increasingly recognized as an important area within nephrology care. Clinicians require awareness of genetic kidney disease to recognize clinical phenotypes, consider use of genomics to aid diagnosis, and inform treatment decisions. Understanding the broad spectrum of clinical phenotypes and principles of genomic sequencing is becoming increasingly required in clinical nephrology, with nephrologists requiring education and support to achieve meaningful patient outcomes. Establishment of effective clinical resources, multi-disciplinary teams and education is important to increase application of genomics in clinical care, for the benefit of patients and their families. Novel applications of genomics in chronic kidney disease include pharmacogenomics and clinical translation of polygenic risk scores. This review explores established and emerging impacts and utility of genomics in kidney disease.

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.

Monogenic and polygenic concepts in chronic kidney disease (CKD)

Kidney function is strongly influenced by genetic factors with both monogenic and polygenic factors contributing to kidney function. Monogenic disorders with primarily autosomal dominant inheritance patterns account for 10% of adult and 50% of paediatric kidney diseases. However, kidney function is also a complex trait with polygenic architecture, where genetic factors interact with environment and lifestyle factors. Family studies suggest that kidney function has significant heritability at 35-69%, capturing complexities of the genome with shared environmental factors. Genome-wide association studies estimate the single nucleotide polymorphism-based heritability of kidney function between 7.1 and 20.3%. These heritability estimates, measuring the extent to which genetic variation contributes to CKD risk, indicate a strong genetic contribution. Polygenic Risk Scores have recently been developed for chronic kidney disease and kidney function, and validated in large populations. Polygenic Risk Scores show correlation with kidney function but lack the specificity to predict individual-level changes in kidney function. Certain kidney diseases, such as membranous nephropathy and IgA nephropathy that have significant genetic components, may benefit most from polygenic risk scores for improved risk stratification. Genetic studies of kidney function also provide a potential avenue for the development of more targeted therapies and interventions. Understanding the development and validation of genomic scores is required to guide their implementation and identify the most appropriate potential implications in clinical practice. In this review, we provide an overview of the heritability of kidney function traits in population studies, explore both monogenic and polygenic concepts in kidney disease, with a focus on recently developed polygenic risk scores in kidney function and chronic kidney disease, and review specific diseases which are most amenable to incorporation of genomic scores.

Factors Associated with Self-Management of Peritoneal Dialysis Patients in Urumqi of Xinjiang of China: A Cross-Sectional Survey

Purpose

To explore the factors associated with self-management of Peritoneal Dialysis (PD) patients and methods of acquiring PD knowledge.

Design

Cross-sectional survey design.

Setting

Urumqi, Xinjiang, China.

Patients

131 Chinese maintenance Peritoneal Dialysis (PD) patients.

Methods

This cross-sectional study was conducted from October 2019 to March 2020 in the First Affiliated Hospital of Xinjiang Medical University of China. 131 PD patients were recruited. Data were collected, including demographic characteristics, clinical dialysis data, self-management ability scale, and methods to obtain PD knowledge. A self-management questionnaire was used for the evaluation of self-management ability.

Results

The score of the self-management ability of PD patients in Xinjiang, China, was (57.6±13.7) points, which was at the middle level in China. There was no statistically significant difference in the self-management ability scores of patients with different ages, sex, ethnicity, marital status, pre-dialysis status, PD time, PD procedures, self-care ability, PD satisfaction, and 24-hour average urine output (P>0.05). There were significant differences in the self-management ability scores of patients with different education levels, occupations, and medical insurance forms (P<0.05). The self-management ability of PD patients was positively correlated with the disease course of uremia and attending lectures on PD knowledge (P<0.05). The main factor affecting self-management ability was education level. There 73.28% of patients considered that it was necessary to establish a WeChat group for PD patients, and 65.7% believed that establishing a WeChat group for PD patients could facilitate communication between patients and enhance treatment confidence.

Conclusion

The study surveyed PD patients who have certain self-management ability. For patients with different education levels, different health education methods should be adopted to promote the improvement of patients' self-management ability. Furthermore, WeChat is essential for Chinese PD patients to obtain disease-related information.

How peritoneal dialysis transforms the peritoneum and vasculature in children with chronic kidney disease-what can we learn for future treatment?

Children with chronic kidney disease (CKD) suffer from inflammation and reactive metabolite-induced stress, which massively accelerates tissue and vascular aging. Peritoneal dialysis (PD) is the preferred dialysis mode in children, but currently used PD fluids contain far supraphysiological glucose concentrations for fluid and toxin removal and glucose degradation products (GDP). While the peritoneal membrane of children with CKD G5 exhibits only minor alterations, PD fluids trigger numerous molecular cascades resulting in major peritoneal membrane inflammation, hypervascularization, and fibrosis, with distinct molecular and morphological patterns depending on the GDP content of the PD fluid used. PD further aggravates systemic vascular disease. The systemic vascular aging process is particularly pronounced when PD fluids with high GDP concentrations are used. GDP induce endothelial junction disintegration, apoptosis, fibrosis, and intima thickening. This review gives an overview on the molecular mechanisms of peritoneal and vascular transformation and strategies to improve peritoneal and vascular health in patients on PD.

The Peritoneal Membrane—A Potential Mediator of Fibrosis and Inflammation among Heart Failure Patients on Peritoneal Dialysis

Peritoneal dialysis is a feasible, cost-effective, home-based treatment of renal replacement therapy, based on the dialytic properties of the peritoneal membrane. As compared with hemodialysis, peritoneal dialysis is cheaper, survival rate is similar, residual kidney function is better preserved, fluid and solutes are removed more gradually and continuously leading to minimal impact on hemodynamics, and risks related to a vascular access are avoided. Those features of peritoneal dialysis are useful to treat refractory congestive heart failure patients with fluid overload. It was shown that in such patients, peritoneal dialysis improves functional status and quality of life, reduces hospitalization rate, and may decrease mortality rate. High levels of serum proinflammatory cytokines and fibrosis markers, among other factors, play an important part in congestive heart failure pathogenesis and progression. We demonstrated that those levels decreased following peritoneal dialysis treatment in refractory congestive heart failure patients. The exact mechanism of beneficial effect of peritoneal dialysis in refractory congestive heart failure is currently unknown. Maintenance of fluid balance, leading to resetting of neurohumoral activation towards a more physiological condition, reduced remodeling due to the decrease in mechanical pressure on the heart, decreased inflammatory cytokine levels and oxidative stress, and a potential impact on uremic toxins could play a role in this regard. In this paper, we describe the unique characteristics of the peritoneal membrane, principals of peritoneal dialysis and its role in heart failure patients.

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.

AQP1 Promoter Variant, Water Transport, and Outcomes in Peritoneal Dialysis

BACKGROUND

Variability in ultrafiltration influences prescriptions and outcomes in patients with kidney failure who are treated with peritoneal dialysis. Variants in AQP1, the gene that encodes the archetypal water channel aquaporin-1, may contribute to that variability.

METHODS

We gathered clinical and genetic data from 1851 patients treated with peritoneal dialysis in seven cohorts to determine whether AQP1 variants were associated with peritoneal ultrafiltration and with a risk of the composite of death or technique failure (i.e., transfer to hemodialysis). We performed studies in cells, mouse models, and samples obtained from humans to characterize an AQP1 variant and investigate mitigation strategies.

RESULTS

The common AQP1 promoter variant rs2075574 was associated with peritoneal ultrafiltration. Carriers of the TT genotype at rs2075574 (10 to 16% of patients) had a lower mean (±SD) net ultrafiltration level than carriers of the CC genotype (35 to 47% of patients), both in the discovery phase (506±237 ml vs. 626±283 ml, P = 0.007) and in the validation phase (368±603 ml vs. 563±641 ml, P = 0.003). After a mean follow-up of 944 days, 139 of 898 patients (15%) had died and 280 (31%) had been transferred to hemodialysis. TT carriers had a higher risk of the composite of death or technique failure than CC carriers (adjusted hazard ratio, 1.70; 95% confidence interval [CI], 1.24 to 2.33; P = 0.001), as well as a higher risk of death from any cause (24% vs. 15%, P = 0.03). In mechanistic studies, the rs2075574 risk variant was associated with decreases in AQP1 promoter activity, aquaporin-1 expression, and glucose-driven osmotic water transport. The use of a colloid osmotic agent mitigated the effects of the risk variant.

CONCLUSIONS

A common variant in AQP1 was associated with decreased ultrafiltration and an increased risk of death or technique failure among patients treated with peritoneal dialysis. (Funded by the Swiss National Science Foundation and others.).