Fenugreek seed ethanolic extract inhibited formation of advanced glycation end products via scavenging reactive carbonyl intermediates

Senescence is a natural phenomenon of growing old. It accelerates under certain conditions like diabetes mellitus resulting in early decline of bodily functions, which can be avoided by many claimed functional foods. The present study aims to investigate the anti-aging ability of Fenugreek seeds (Trigonellafoenum-graecum); a common ingredient of Indo-Pak cuisines. Briefly, the Fenugreek seeds extract (FgSE) in concentrationsof0.1, 0.5 and 1 mg/ml inhibited the formation of Advanced Glycation End products (AGEs) and fructosamine adducts in Bovine serum albumin (BSA)/fructose model in vitro. The BSA conformational analysis via Circular Dichorism and Congo red assays showed that it preserves secondary structure of BSA in aforementioned model. Although mechanistic studies revealed insignificant lysine blocking ability of Fenugreek by OPA assay, however carbonyl entrapping was found to be 24%, 34% and 42% at 0.1, 0.5 and 1 mg/ml, respectively. In vivo model of High Fructose diet (HFD) induced glycation, FgSE treatment in doses of 10, 25 & 50 mg/kg markedly improved Escape latency (p < 0.01) and preserved cognition in Morris Water Maze. Our data further exhibits significant decrease of CML (Nε-carboxymethyl lysine) levels in serum and hippocampus byFgSE treatment in comparison with HFD group. Therefore, we deduced that FgSE prevents glycation-induced memory decline via entrapping the reactive carbonyl intermediates, formed during production of AGEs. Hence, as a promising functional food it slows down the harmful process of glycation and aging associated morbidities.

Methylglyoxal induces stress signaling and promotes the germination of maize at low temperature

Maize is sensitive to cold injury, especially during germination. Since cold causes oxidative stress, compounds that promote the accumulation of free radical forms, such as the reactive aldehyde (RA) methylglyoxal (MG), may be suitable to trigger a systemic defense response. In this study, maize seeds were soaked in MG solution for one night at room temperature, before germination test at 13°C. The exogenous MG enhanced the germination and photosynthetic performance of maize at low temperature. Transcriptome analysis, hormonal, and flavonoid profiling indicated MG-induced changes in photosystem antenna proteins, pigments, late embryogenesis abundant proteins, abscisic acid (ABA) derivatives, chaperons, and certain dihydroflavonols, members of the phenylpropanoid pathway. MG-response of the two maize cultivars (A654 and Cm174) were somewhat different, but we recorded higher endogenous hydrogen peroxide (H₂ O₂ ) and lower nitric oxide (NO) level in at least one of the treated genotypes. These secondary signal molecules may provoke some of the changes in the hormonal, metabolic and gene expression profile. Decreased auxin transport, but increased ABA degradation and cytokinin and jasmonic acid (JA) synthesis, as well as an altered carbohydrate metabolism and transport (amylases, invertases, and SWEET transporters) could have promoted germination of MG-pretreated seeds. While LEA accumulation could have protected against osmotic stress and catalase expression and production of many antioxidants, like para-hydroxybenzoic acid (p-HBA) and anthocyanins may have balanced the oxidative environment for maize germination. Our results showed that MG-pretreatment could be an effective way to promote cold germination and its effect was more pronounced in the originally cold-sensitive maize genotype.

Comparison of Longitudinal Membrane Function in Peritoneal Dialysis Patients According to Dialysis Fluid Biocompatibility

Introduction

Preservation of peritoneal function is essential in long-term peritoneal dialysis. Biocompatible dialysis solutions might prevent or postpone the membrane alteration resulting in ultrafiltration failure and consecutive morbidity and mortality.

Methods

We conducted an observational cohort study in which we made a longitudinal comparison between the course of peritoneal solute and fluid transport during treatment with conventional and biocompatible solutions. Therefore, prospectively collected peritoneal transport data from the yearly standard peritoneal permeability analysis were analyzed in 251 incident patients treated between 1994 and censoring in 2016. Fluid transport included small pore and free water transport. Solute transport was assessed by creatinine mass transfer area coefficient and glucose absorption. Linear mixed models including change point analyses were performed. Interaction with peritonitis was examined.

Results

One hundred thirty-five patients received conventional and 116 biocompatible solutions. Sixty-seven percent (conventional) and 64% (biocompatible) of these underwent minimally three transport measurements. Initially, biocompatible fluids showed higher small solute transport and lower ultrafiltration than conventional fluids up to 3 years. Thereafter, conventional fluids showed an increase in small solute transport (+2.7 ml/min per year; 95% confidence interval [CI]: 0.9 to 4.5) and a decrease of free water transport (−28.0 ml/min per year; 95% CI: −60.4 to 4.4). These were minor or absent in biocompatible treatment. Peritonitis induced a decrease of transcapillary ultrafiltration after 2 years on dialysis with conventional solutions (−291 ml/min per year; 95% CI: −550 to −32) while this was absent in biocompatible treatment.

Conclusion

Despite a higher initial solute transport with biocompatible solutions, these have less influence on functional long-term peritoneal alterations than conventional solutions.

Glucose Degradation Products and Peritoneal Membrane Function

Background

The bioincompatibility of peritoneal dialysis fluids (PDF) in current use has been partially attributed to the presence of glucose degradation products (GDPs), which are generated during heat sterilization of PDF. Several of the GDPs have been identified and we have recently demonstrated that these GDPs per se may impair the viability and function of human peritoneal mesothelial cells (HPMC) in vitro. It is also possible that GDP-related toxicity is further exacerbated by the milieu of PDF. We review the current literature on GDP and present the results of experiments comparing the impact of heat- and filter-sterilized PDF on the viability and function of HPMC.

Methods

Peritoneal dialysis fluids with low (1.5%) and high (4.25%) glucose concentrations were laboratory prepared according to the standard formula and sterilized either by heat (H-PDF; 121°C, 0.2 MPa, 20 minutes) or filtration (F-PDF; 0.2 μ). The buildup of GDP was confirmed by UV absorbance at 284 nm. Confluent HPMC monolayers were exposed to these solutions mixed 1:1 with standard M199 culture medium. After 24 hours, cell viability was assessed with the MTT assay, and interleukin-1β–stimulated monocyte chemotactic protein-1 (MCP-1) release with specific immunoassay.

Results

Exposure of HPMC to H-PDF resulted in a significant decrease in cell viability, with solutions containing 4.25% glucose being more toxic than 1.5% glucose-based PDF (27.4% ± 3.4% and 53.4% ± 11.0% of control values, respectively). In contrast, viability of HPMC exposed to F-PDF was not different from that of control cells. Moreover, treatment with H-PDF impaired the release of MCP-1 from HPMC to a significantly greater degree compared to F-PDF (17.4% and 24.9% difference for low and high glucose PDF, respectively).

Conclusions

Exposure of HPMC to H-PDF significantly impairs cell viability and the capacity for generating MCP-1 compared to F-PDF. This effect is likely to be mediated by GDPs present in H-PDF but not in F-PDF.

How to Reduce 3-Deoxyglucosone and Acetaldehyde in Peritoneal Dialysis Fluids

Objective

3-Deoxyglucosone (3-DG) and acetaldehyde were found to be the major reactive carbonyl compounds in conventional heat-sterilized peritoneal dialysis fluids (PDFs). The aim of this study was to identify factors in the production of PDFs promoting or inhibiting the formation of acetaldehyde and 3-DG.

Design

Single-chamber bag PDFs with different buffer systems and pH values were analyzed for acetaldehyde. 3-Deoxyglucosone was determined in double-chamber bag PDFs with different pH values, in commercially available samples, and in double-chamber products stored under defined conditions.

Results

Acetaldehyde was found in the presence of lactate and malate, whereas in 2-hydroxybutanoate-buffered solution propionaldehyde was detected instead. Between pH 5.0 and 6.0 the acetaldehyde content in lactate-buffered solutions increased strongly. The concentration of 3-DG in the chamber containing glucose in double-chamber bags increased between pH 3.0 and 5.0 by a factor of 6. 3-Deoxyglucosone concentrations in commercially available products vary greatly, reflecting the different pH values of these products. A time- and temperature-dependent reaction leads to a reduction in 3-DG and an increase in 5-hydroxymethyl-furan-2-carbaldehyde during storage.

Conclusion

Acetaldehyde is produced by a reaction that requires both lactate and glucose. Thus, its formation can be prevented by a separation of the reaction partners, glucose and lactate, in a double-chamber bag. In double-chamber bags, pH greatly influences the formation of 3-DG. Minimal formation is observed in the region of pH 3.0. This finding should be taken into account for the development of new double-chamber bag PDFs.

Influence of Icodextrin on Plasma and Dialysate Levels of N∊-(Carboxymethyl)Lysine and N∊-(Carboxyethyl)Lysine

Rationale

Standard peritoneal glucose solutions may induce the formation of advanced glycation end products (AGEs). Preliminary data suggest that AGE formation may be less with the use of polyglucose solutions (icodextrin). Therefore, we investigated whether the use of icodextrin for the long dwell would result in a reduction in plasma and dialysate levels of the AGE products N∊-(carboxymethyl) lysine (CML) and N∊-(carboxyethyl)lysine (CEL).

Patients and Methods

40 patients were randomized to treatment with standard glucose solutions (1.36%) and icodextrin for the long dwell during a 4-month study period; 32 patients completed the study. CML was assessed by stable isotope dilution/tandem mass spectrometry.

Results

CML levels in plasma increased significantly in patients treated with icodextrin (0.146 ± 0.056 at start vs 0.188 ± 0.069 μmol/mmol Lys at the end of the study, p < 0.0001) but did not change in the control group (0.183 ± 0.090 vs 0.188 ± 0.085 μmol/mmol Lys). The same held true for CML levels in dialysate (0.28 ± 0.09 at start vs 0.33 ± 0.11 μmol/mmol Lys at the end of the study, p < 0.025). No change was observed in patients treated with the control solutions (0.31 ± 0.11 at start vs 0.31 ± 0.07 μmol/mmol Lys).

Conclusion

Contrary to the hypothesis, plasma and dialysate levels of CML increased in patients treated using icodextrin for the long dwell.

Impact of Glucose in Peritoneal Dialysis: Saint or Sinner?

Peritoneal dialysis (PD) solutions using glucose as osmotic agent have been used for more than two decades as effective treatment for patients with end-stage renal disease. Although alternative osmotic agents such as amino acids and macromolecular solutions, including polypeptides and glucose polymers, are now available, glucose is still the most widely used osmotic agent in PD. It has been shown to be safe, effective, readily metabolized, and inexpensive. On the other hand, it is widely assumed that exposure of the peritoneal membrane to high glucose concentrations contributes to both structural and functional changes in the dialyzed peritoneal membrane. As in diabetes, glucose, either directly or indirectly through the generation of glucose degradation products or the formation of advanced glycation end products, may contribute to peritoneal membrane failure. Although efforts to reduce glucose toxicity have been made for years, only a few suggestions, such as dual-bag systems with bicarbonate as buffer system, have found broader acceptance. Recently, some interesting new approaches to the problem of glucose-related toxicity have been made, but further investigations will be necessary before they can be used clinically. This review will focus on adverse effects of glucose in PD solutions and summarize different aspects of glucotoxicity and potential therapeutic interventions.

Early Glycated Albumin, but Not Advanced Glycated Albumin, Methylglyoxal, or 3-Deoxyglucosone Increases the Expression of Pai-1 in Human Peritoneal Mesothelial Cells

Objective

The continuous contact of glucose-containing peritoneal dialysis (PD) fluids with the peritoneum results in the intraperitoneal formation of early and advanced glycation end-products. This nonenzymatic glycation of proteins may cause morphological and functional alterations to the peritoneum, which may contribute to patient dropout from PD therapy. Because fibrinolytic system components have been demonstrated to play an important role in the balance of intraperitoneal generation and degradation of fibrin, we studied the effect of early and advanced glycated human serum albumin, methylglyoxal, and 3-deoxyglucosone on the synthesis of tissue-type plasminogen activator (tPA), as well as its specific inhibitor (PAI-1), in human peritoneal mesothelial cells (HPMC).

Methods

Antigen concentrations in the supernatants of cultured HPMC were measured by ELISA. Northern blot analysis was conducted for mRNA expression. Electrophoretic mobility shift assays were applied to demonstrate the involvement of the transcription factors nuclear factor kappa B (NF-κB) and activator protein-1 (AP-1) in signal transduction.

Results

Incubation of HPMC with early glycated albumin (GHSA) resulted in a time- and concentration-dependent increase in PAI-1 mRNA expression and antigen secretion. In contrast, no changes in PAI-1 synthesis occurred after stimulation with either the 1,2-dicarbonyl compounds methylglyoxal and 3-deoxyglucosone, or with late advanced glycation end-products. tPA synthesis was not affected by any of the tested components. Furthermore, HPMC exposed to GHSA induced NF-κB and AP-1 DNA binding activity, suggesting that GHSA-induced over-expression of PAI-1 is transcriptionally regulated by both transcription factors.

Conclusions

We conclude that Amadori modified glycated albumin upregulates PAI-1 synthesis in HPMC, possibly mediated through the activation of the transcription factors NF-κB and AP-1. The present data support the clinical relevance of the formation of glycated proteins and their involvement in pathological processes in PD patients. Thus, glycated albumin may contribute to an imbalance between intraperitoneal formation and degradation of fibrin that causes peritoneal structural alterations, with subsequent membrane failure.

The Choice of Dialysis Solutions in Pediatric Chronic Peritoneal Dialysis: Guidelines by AnAD HOCEuropean Committee

Objective

To provide guidelines on choosing dialysis solutions for children on chronic peritoneal dialysis (PD).

Setting

European Paediatric Peritoneal Dialysis Working Group.

Data Source

Literature on the application of PD solutions in children ( Evidence), and discussions within the group ( Opinion).

Conclusions

Glucose is the standard osmotic agent for PD in children ( Evidence). The lowest glucose concentration needed should be used ( Opinion). Low calcium solution (1.25 mmol/L) should be applied, wherever possible, with careful monitoring of parathyroid hormone levels ( Opinion). The use of amino acid-containing dialysis fluids can be considered in malnourished children, although aggressive enteral nutrition is preferred ( Opinion). There is insufficient evidence documenting the efficacy of intraperitoneally administered amino acids ( Evidence). When ultrafiltration and/or solute removal are insufficient, poly-glucose solutions are a welcome addition to the treatment of children on nocturnal intermittent PD ( Evidence). However, in the absence of any reported long-term experience with children, their use must be closely monitored ( Opinion). Bicarbonate would appear to be the preferred buffer for PD in children, but more in vivo studies are required before it replaces the present lactate-containing solutions ( Evidence/Opinion).

Chemical and Immunological Characterization of Oxidative Nonenzymatic Protein Modifications in Dialysis Fluids

← Background

Glucose degradation products (GDP) in dialysis fluids may induce nonenzymatic protein modifications, the chemical nature and biological properties of which should be better defined.

← Aims

To characterize nonenzymatic protein modifications present in glucose-based peritoneal dialysis fluids (PDF) and to evaluate the relationship between concentrations of GDP and the derived nonenzymatic modifications, and the potential of PDF for generating these modifications in vitro.

← Methods

The presence, distribution, and content of several nonenzymatic protein modifications in PDF were evaluated by immunological methods, by HPLC, and by gas chromatography-mass spectrometry (GC/MS). Peritoneal dialysis fluid-induced oxidative stress in cells was evaluated by flow cytometry. The potential of PDF for generating oxidative and glycoxidative modifications was examined by immunological and cross-linking analyses.

← Results

The albumin present in PDF is modified by carboxymethyllysine (CML). GC/MS analyses of PDF proteins confirmed the presence of CML and demonstrated the occurrence of carboxyethyllysine, malondialdehyde lysine, and oxidation-derived semialdehydes. Furthermore, their concentrations in PDF proteins were significantly higher than those in plasma proteins (in all cases, p < 0.02). The concentration of pyrraline, a non-oxidative advanced glycation end-product, increased with dwell time up to 6 hours ( p < 0.03). The PDF induced cellular free-radical production, which was partially inhibited by the Maillard reaction inhibitor aminoguanidine ( p < 0.001). The potential to generate oxidative and glycoxidative modifications demonstrated an inverse relationship with dwell time ( p < 0.05). The PDF was able to induce collagen cross-linking in a close relationship with GDP concentration.

← Conclusions

( 1 ) PDF contains non-oxidative and several oxidative nonenzymatic protein modifications in higher concentrations than plasma. ( 2 ) Peritoneal dialysis fluid induces oxidative stress in vitro, which can be partially inhibited by aminoguanidine. ( 3 ) These properties are directly related to GDP concentration. ( 4 ) Peritoneal dialysis fluid is able to generate glycoxidative and oxidative damage to proteins in vitro in a dwell-time dependent fashion.

Single Exposure of Mesothelial Cells to Glucose Degradation Products (GDPs) Yields Early Advanced Glycation End-Products (AGEs) and a Proinflammatory Response

← Background

Fluids commonly used for peritoneal dialysis (PD) have a low pH and a high glucose content. Furthermore, heat sterilization of dialysis fluids degrades some of the glucose into glucose degradation products (GDPs), such as methylglyoxal (MGO) and 3-deoxyglucosone (3-DG). Mesothelial cells (MCs) form the first line in the peritoneal cavity and are constantly exposed to these nonphysiological conditions. Since MCs play an important role in the regulation of inflammatory responses in the peritoneal cavity, we studied the kinetics of MC uptake of highly purified GDP species, along with their effect on various cellular biological and immunological parameters.

← Methods

Methylglyoxal and 3-DG were purified and added to MC cultures. Complexing to medium components or uptake by MCs was analyzed over time by HPLC of the culture supernatant and by immunocytochemistry of MCs for MGO-modified proteins. Furthermore, MCs were exposed to a single dose of MGO or 3-DG and analyzed for apoptosis, proliferation by MTT assay, and [3H]-thymidine incorporation. Incorporation of [35S]-methionine was determined in order to analyze de novo protein synthesis. Expression of the adhesion molecules intercellular adhesion molecule-1 (ICAM-1), CD44, and vascular cell adhesion molecule-1 (VCAM-1) was analyzed by cell-bound ELISA. Effects of MGO and 3-DG on cytokine production were also analyzed.

← Results

Substitution of MGO and 3-DG in culture medium resulted in a spontaneous decrease in MGO over time, whereas 3-DG levels decreased minimally. The concentration of these GDPs was more reduced in the presence of MCs, indicating binding to and/or uptake by MCs of these GDPs. Mesothelial cells that had been cultured in the presence of MGO showed positive staining with a monoclonal that specifically recognizes MGO-modified proteins, demonstrating complexing to mesothelial cellular proteins. Cell-bound ELISA showed a two- to threefold induction of expression of VCAM-1 by MGO and 3-DG; the expression of ICAM-1 and CD44 was not changed. Mesothelial cells showed a twofold increase in interleukin (IL)-6 and IL-8 production after exposure to 3-DG. Furthermore, incubation with MGO and 3-DG induced apoptosis and reduced the proliferation of cells, but did not influence protein synthesis.

← Conclusions

In the current report we demonstrate that MCs take up MGO and 3-DG and form early advanced glycation end-products. Upon short exposure to a single GDP, MCs react with enhanced cytotoxic damage and a proinflammatory response, evidenced by increased VCAM-1 expression and elevated production of IL-6 and IL-8.

Glucose Degradation Products and the Peritoneal Mesothelium

Conventional heat-sterilized, glucose-based peritoneal dialysis (PD) fluids contain significant amounts of glucose degradation products (GDPs) such as aldehydes and dicarbonyl compounds (glyoxal, methylglyoxal). These GDPs have been shown to impair cell functions in various in vitro experimental models. In peritoneal mesothelial cells, GDPs dose-dependently inhibit cell proliferation and mediator synthesis. In addition, some GDPs potently promote generation of advanced glycation end-products (AGEs). Immunohistochemistry finds AGEs in the peritoneal membrane of chronic continuous ambulatory peritoneal dialysis (CAPD) patients, suggesting that peritoneal AGE accumulation may be involved in chronic peritoneal fibrosis.

The formation of GDPs might be prevented by filter-sterilization of PD fluids. Another option is to separate the glucose and the buffer system in dual-chambered or multi-chambered containers. In these systems, the glucose is kept in a separate compartment at high concentration and very low pH—both conditions being known to minimize the degree of glucose decomposition during autoclaving. Initial experimental evidence suggests that these novel, multi-chambered fluids significantly improve in vitro biocompatibility; however, the clinical relevance of these results remains to be established in clinical trials.

Biocompatibility of New Peritoneal Dialysis Solutions: What Can We Hope to Achieve?

Despite the bioincompatibility of the “old”, standard, high glucose, lactate-buffered peritoneal dialysis (PD) solutions, PD is itself a highly successful dialysis modality with patient survival equivalent to that of hemodialysis (HD) during the initial 3 – 5 years of dialysis therapy. Nevertheless, PD technique survival is often limited by infectious complications and alterations in the structure and function of the peritoneal membrane. These local changes also have a negative impact on patient survival owing to systemic effects such as those often seen in patients with high peritoneal transport rate and loss of ultrafiltration (UF) capacity.

Patient mortality remains unacceptably high in both HD and PD patients, with most premature deaths being associated with signs of malnutrition, inflammation, and atherosclerotic cardiovascular disease (MIA syndrome). These systemic signs are likely to be influenced by PD solutions both directly and indirectly (via changes in the peritoneal membrane). New, biocompatible PD solutions may have favorable local effects (viability and function of the peritoneal membrane) and systemic effects (for example, on MIA syndrome). Amino acid–based solution [Nutrineal (N): Baxter Healthcare Corporation, Deerfield, IL, U.S.A.] may improve nutritional status as well as peritoneal membrane viability. Bicarbonate/lactate–buffered solution [Physioneal (P): Baxter Healthcare Corporation] may ameliorate local and systemic effects of low pH, high lactate, and high glucose degradation products. Icodextrin-based solution [Extraneal (E): Baxter Healthcare SA, Castlebar, Ireland] may improve hypertension and cardiovascular problems associated with fluid overload and may extend time on therapy in patients with loss of UF capacity.

The positive effects of each of these new, biocompatible solutions have been demonstrated in several studies. It is likely that the combined use of N, P, and E solutions will produce favorable synergies in regard to both local effects (peritoneal viability) and systemic effects (less malnutrition, inflammation, and fluid overload). Solution combination is an exciting area for clinical study in the coming years. Furthermore, dialysis fluid additives such as hyaluronan, which protects and improves the function of the peritoneal membrane, may further improve PD solutions. The new, biocompatible PD solutions represent an entirely new era in the evolution of the PD therapy; they are likely to have markedly positive effects on both PD technique and PD patient survival in coming years.

Amadori Albumin and Advanced Glycation End-Product Formation in Peritoneal Dialysis using Icodextrin

Objective

To study the influence of peritoneal dialysis (PD) solutions on the formation of early glycated products and advanced glycation end-products (AGEs).

Design and Patients

The formation of both Amadori albumin and AGEs in glucose- and icodextrin-based PD fluids was analyzed in vitro and in peritoneal effluents of continuous cyclic peritoneal dialysis (CCPD) patients.

Results

Albumin incubated with glucose-based PD fluids showed a time- and glucose concentration-dependent formation of Amadori albumin and AGEs. Aminoguanidine completely inhibited AGE but not Amadori albumin formation. Albumin incubated in icodextrin resulted in the lowest levels of Amadori albumin and AGE. Amadori albumin levels in effluents of 24 CCPD patients (12 glucose and 12 icodextrin for their daytime dwells) were similar. Dialysate samples collected during a mass transfer area coefficient test in 16 CCPD patients (8 glucose, 8 icodextrin) showed an increase in Amadori albumin formation from baseline ( p < 0.0001), without a difference between the groups. In the total group, there was a positive relationship between duration on PD and dialysate Amadori albumin concentration at 240 minutes ( p = 0.03). The Amadori albumin dialysate-to-plasma (D/P) ratio at 240 minutes was 0.82 ± 0.11, and its clearance amounted to 7.71 ± 1.14 mL/min, while the albumin D/P ratio was 0.010 ± 0.003 and its clearance was 0.089 ± 0.017 mL/min. In a peritoneal biopsy of a CCPD patient, Amadori albumin was observed in the mesothelial layer and the endothelium of the peritoneum.

Conclusions

Using icodextrin-based instead of glucose-based PD fluids can largely reduce the formation of Amadori albumin and AGEs. However, CCPD patients using icodextrin during daytime dwells do not have lower effluent levels of Amadori albumin and AGEs, probably due to the exposure to glucose during their nighttime exchanges. Kinetic studies suggest washout of locally produced Amadori albumin.

Better Preservation of the Peritoneum in Rats Exposed to Amino Acid-Based Peritoneal Dialysis Fluid

Background

Glucose-containing peritoneal dialysis fluids (PDF) show impaired biocompatibility, which is related partly to their high glucose content, presence of glucose degradation products, low pH, and lactate buffer, or a combination of these factors. In a rat chronic peritoneal exposure model, we compared effects of an amino acid-based PDF (AA-PDF) with a glucose-containing PDF on the peritoneal microcirculation and morphology.

Method

Two groups of rats received 10 mL of either fluid daily for 5 weeks via peritoneal catheters connected to implanted subcutaneous mini vascular access ports. Leukocyte–endothelium interactions in the mesenteric venules were investigated by intravital microscopy. Quantification of angiogenesis and fibrosis and inspection of the mesothelial cell layer were performed by light and electron microscopy.

Results

Daily exposure to glucose-containing PDF resulted in a significant increase in the number of rolling leukocytes in mesenteric venules, whereas instillation of AA-PDF did not change the level of leukocyte rolling. Glucose-containing PDF evoked a significantly higher number of milky spots in the omentum, whereas this response was significantly reduced in animals exposed to the AA-PDF ( p < 0.02). Chronic instillation of glucose-containing PDF induced angiogenesis in various peritoneal tissues, accompanied by fibrosis in the mesentery and parietal peritoneum. Quantitative morphometric evaluation of omentum and mesentery showed a clear trend toward less angiogenesis after treatment with the AA-PDF compared to the glucose-containing PDF, which reached statistical significance in the parietal peritoneum ( p < 0.04). Instillation of AA-PDF resulted in approximately 50% reduction of fibrosis in the mesentery ( p < 0.04) and approximately 25% reduction in the parietal peritoneum ( p < 0.009) compared to glucose-containing PDF. Glucose-containing PDF damaged the mesothelial cell layer, whereas the mesothelium was intact after AA-PDF treatment, as evidenced by electron microscopy.

Conclusion

Our data in a rat chronic peritoneal exposure model clearly demonstrate reduced immune activation (evidenced by decreased number of rolling leukocytes and decreased induction of omental milky spots) and reduced neoangiogenesis, fibrosis, and mesothelial damage of the peritoneal membrane after treatment with AA-PDF compared to glucose-containing PDF.

Take Care in how you Store Your PD Fluids: Actual Temperature Determines the Balance between Reactive and Non-Reactive GDPs

Objective

During heat sterilization and during prolonged storage, glucose in peritoneal dialysis fluids (PDF) degrades to carbonyl compounds commonly known as glucose degradation products (GDPs). Of these, 3,4-dideoxyglucosone-3-ene (3,4-DGE) is the most cytotoxic. It is an intermediate in degradation between 3-deoxyglucosone (3-DG) and 5-hydroxymethyl-2-furaldehyde (5-HMF). We have earlier reported that there seems to be equilibrium between these GDPs in PDF. The aim of the present study was to investigate details of this equilibrium.

Methods

Aqueous solutions of pure 3-DG, 3,4-DGE, and 5-HMF were incubated at 40°C for 40 days. Conventional and low-GDP fluids were incubated at various temperatures for up to 3 weeks. Formaldehyde, acetaldehyde, glyoxal, methylglyoxal, 3-DG, 3,4-DGE, and 5-HMF were analyzed using high performance liquid chromatography.

Results

Incubation of 100 μmol/L 3,4-DGE resulted in the production of 36 μmol/L 3-DG, 4 μmol/L 5-HMF, and 40 μmol/L unidentified substances. With the same incubation, 200 μmol/L 3-DG was converted to 9 μmol/L 3,4-DGE, 6 μmol/L 5-HMF, and 14 μmol/L unidentified substances. By contrast, 100 μmol/L 5-HMF was uninfluenced by incubation. In a conventional PDF incubated at 60°C for 1 day, the 3,4-DGE concentration increased from 14 to a maximum of 49 μmol/L. When the fluids were returned to room temperature, the concentration decreased but did not reach original values until after 40 days. In a low GDP fluid, 3,4-DGE increased and decreased in the same manner as in the conventional fluid but reached a maximum of only 0.8 μmol/L.

Conclusions

Considerable amounts of 3,4-DGE may be recruited by increases in temperature in conventional PDFs. Lowering the temperature will again reduce the concentration but much more time will be needed. Precursors for 3,4-DGE recruitment are most probably 3-DG and the enol 3-deoxyaldose-2-ene, but not 5-HMF. Considering the ease at which 3,4-DGE is recruited from its pool of precursors and the difficulty of getting rid of it again, one should be extremely careful with the temperatures conventional PDFs are exposed to.

PD Fluids Contain High Concentrations of Cytotoxic GDPs Directly after Sterilization

Objective

Glucose degradation products (GDPs) in peritoneal dialysis (PD) fluids are cytotoxic and affect the survival of the peritoneal membrane. One of the most reactive GDPs in PD fluids is 3,4-dideoxyglucosone-3-ene (3,4-DGE). 3,4-DGE has been reported as an intermediate between 3-deoxyglucosone (3-DG) and 5-hydroxymethyl furaldehyde (5-HMF) during degradation of glucose. In PD fluids, 3,4-DGE exists in a temperature-dependent equilibrium with a pool of unidentified substances. The aim of this study was to explore this equilibrium and its temperature dependence during the first months of storage after the sterilization procedure.

Methods

GDPs and inhibition of cell growth (ICG) were measured directly after sterilization of the PD fluid and during storage at different temperatures for 60 days. The following GDPs were analyzed: 3-DG, 3,4-DGE, 5-HMF, formaldehyde, acetaldehyde, glyoxal, and methylglyoxal.

Results

Immediately after sterilization, the concentration of 3,4-DGE was 125 μmol/L. During the first weeks of storage, it decreased by about 80%. At the same time, the 3-DG concentration increased. None of the other GDPs were significantly affected. Cytotoxicity correlated well with the concentration of 3,4-DGE. When pure 3,4-DGE was substituted for the lost amount of 3,4-DGE after 30 days of storage, the initial ICG was almost completely regained.

Conclusions

Heat sterilization of PD fluids promotes the formation of large quantities of 3,4-DGE, rendering the fluid highly cytotoxic. During storage, the main part of 3,4-DGE is reversibly converted in a temperature-dependent manner to a less cytotoxic pool, consisting mainly of 3-DG. Cytotoxicity seems to be dependent exclusively on 3,4-DGE. In order to avoid higher levels of 3,4-DGE concentrations, PD fluids should not be used too soon after sterilization and should not be stored at temperatures above room temperature.

Biological Significance of Reducing Glucose Degradation Products in Peritoneal Dialysis Fluids

Carbohydrates are not stable when exposed to energy; they degrade into new molecules. In peritoneal dialysis (PD) fluids, degradation of glucose occurs during the heat sterilization procedure. The biological consequences of this degradation are side effects such as impaired proliferation and impaired host defense mechanisms, demonstrated in vitro for a great variety of cells.

Several highly toxic compounds—such as formaldehyde and 3-deoxyglucosone—have been identified in PD fluids. Carbonyl compounds, apart from being cytotoxic, are also well-known promoters of irreversible advanced glycation end-products (AGEs), which might participate in the long-term remodeling of the peritoneal membrane.

Various approaches can be used to reduce the formation of glucose degradation products (GDPs) during heat sterilization. Some examples are shortening the sterilization time, lowering the pH, removing catalyzing substances, and increasing glucose concentration. The latter three factors are employed in the multi-compartment bag with a separate chamber containing pure glucose at high concentration and low pH.

Gambrosol trio, a PD fluid produced in this way, shows reduced cytotoxicity, normalized host defense reactions, less AGE formation, and reduced concentrations of formaldehyde and 3-deoxyglucosone. Moreover, in the clinical situation, the fluid turns out to be more biocompatible for the patient, causing less mesothelial cell damage, which in the long term could lead to a more intact peritoneal membrane.

Conclusion

Glucose degradation products in heat-sterilized fluids for peritoneal dialysis are cytotoxic, promote AGE formation, and cause negative side effects for the patient. Using improved and well-controlled manufacturing processes, it is possible to produce sterile PD fluids with glucose as the osmotic agent but without the negative side effects related to GDPs.

FirstIn VitroandIn VivoExperiences with Stay·Safe Balance, A pH-Neutral Solution in a Dual-Chambered Bag

In addition to low pH and high osmolarity, glucose degradation products (GDPs) are considered to play a major role in the bioincompatibility of peritoneal dialysis fluids (PDFs). The formation of GDPs can be reduced by separating the glucose component of the solution (kept at very low pH) from the lactate component of the solution (kept at alkaline pH) during sterilization and storage. This development has been achieved by the use of a dual-chambered bag. Immediately before infusion, the seam between the two chambers is opened, and the contents are mixed. The result is a fluid with a more physiologic pH in the range 6.8 – 7.4.

Concentrations of 3-deoxyglucosone (3-DG), methyl-glyoxal (MG), acetaldehyde (AA), and formaldehyde (FA) in Stay·Safe Balance (Fresenius Medical Care, Bad Homburg, Germany) were remarkably reduced when compared to conventional PD solution [conventional PDF (1.5% glucose): 172 μmol/L, 6 μmol/L, 152 μmol/L, and 7 μmol/L respectively; Stay·Safe Balance (1.5% glucose): 42 μmolL, < 1 μmol/L, < 2 μmol/L, and < 3 μmol/L respectively; conventional PDF (4.25% glucose): 324 μmol/L, 10 μmol/L, 182 μmol/L, and 13 μmol/L respectively; Stay·Safe Balance (4.25% glucose): 60 μmol/L, < 1 μmol/L, < 2 μmol/L, and < 3 μmol/L respectively).

Human peritoneal mesothelial cells (HPMCs) were exposed to a control solution, a conventional PDF [CAPD 2, 1.5% glucose (Fresenius Medical Care, Bad Homburg, Germany)], and Stay·Safe Balance, either in a co-incubation model (24-hour PDF exposure) or in a pre-incubation model (30-min PDF exposure), followed by 24-hour recovery in culture medium. Interleukin-1β (IL-1β)–stimulated (1 ng/mL) IL-6 secretion from HPMCs was assessed by ELISA. Exposure of HPMCs to conventional PDF resulted in a significant reduction in IL-6 release, which was fully restored following exposure to Stay·Safe Balance. In addition to the short-term investigations, long-term in vitro studies were also carried out. All fluids had near-neutral pH and were changed every second day. After 1, 3, 5, 7, 10, and 13 days of exposure, cell viability was assessed. Whereas exposure to conventional PDF resulted in a significant reduction in HPMC viability after just 3 – 5 days, no significant toxicity of filter-sterilized or dual-chambered fluid was observed for up to 13 days.

An observational study with 9 patients suggested that the efficacy of Stay·Safe Balance is equivalent to that of conventional solution. However, even short-term treatment (8 ± 1 weeks) with this more biocompatible solution seems to improve mesothelial cell mass as indicated by a rise in cancer antigen 125 (CA125) from a baseline of 47 ± 37 U/ min to 172 ± 90 U/min.

Our data indicate that Stay·Safe Balance may help to better preserve peritoneal membrane cell function. An ongoing European multicenter study is expected to confirm these results.

Glucose Degradation Products in Peritoneal Dialysis Fluids May Have Both Local and Systemic Effects: A Study of Residual Fluid and Mesothelial Cells

Objective

When peritoneal dialysis (PD) fluids are heat sterilized, glucose is degraded to carbonyl compounds. These compounds are known to interfere with many cellular functions and to promote the formation of advanced glycation end-products. However, little is known about what actually happens with glucose degradation products (GDPs) after infusion into the peritoneal cavity. The aim of the present study was to investigate possible targets for GDPs in the peritoneal cavity.

Design

In vitro reactions between residual fluid and GDPs were studied by incubating unused PD fluid with overnight dialysate. Confluent monolayer cultures of human mesothelial cells were used as a model to study the reactions of GDPs with the cells lining the peritoneal cavity.

Methods

Samples were analyzed, using high pressure liquid chromatography, for the presence of formaldehyde, acetaldehyde, 5-hydroxymethyl-2-furaldehyde (5-HMF), methylglyoxal, and 3-deoxyglucosone (3-DG). Cytotoxicity was determined as inhibition of proliferation of cultured fibroblasts.

Results

None of the analyzed GDPs reacted with overnight dialysate. Formaldehyde and methylglyoxal, in contrast to 3-DG and 5-HMF, reacted with the cultured mesothelial cells.

Conclusions

Low molecular weight carbonyls such as formaldehyde and methylglyoxal most probably react with the mesothelial cells lining the peritoneal cavity, and could be responsible for the disappearance of these cells during long-term treatment. 3-Deoxyglucosone showed remarkably low reactivity and was most probably transported within the patient.

3,4-DGE in Peritoneal Dialysis Fluids Cannot be Found in Plasma after Infusion into the Peritoneal Cavity

Objective

Glucose degradation products (GDPs) are important in the outcome of peritoneal dialysis (PD) treatment. 3,4-dideoxyglucosone-3-ene (3,4-DGE) is the most cytotoxic GDP found in conventionally manufactured fluids and may, in addition, be recruited from 3-deoxyglucosone (3-DG). It is not known what happens with those GDPs in patients during PD. The aim of this study was to investigate if the 3,4-DGE and 3-DG in PD fluids can be found in plasma during treatment.

Design

PD patients were dialyzed with a conventional PD fluid containing 43 μmol/L 3,4-DGE and 281 μmol/L 3-DG. Parallel experiments were performed in rats as well as in vitro with human plasma. The rats were dialyzed with a PD fluid containing 100 μmol/L 3,4-DGE and 200 μmol/L 3-DG.

Results

The concentration of 3,4-DGE in the peritoneum decreased at a much higher rate than 3-DG during the dwell. 3,4-DGE was not, however, detected in the plasma of patients or rats during dialysis. The concentration of 3-DG in plasma peaked shortly after infusion of the fluid to the peritoneal cavity. The concentration of 3,4-DGE during experimental incubation in plasma decreased rapidly, while the concentration of 3-DG decreased only 10% as rapidly or less.

Conclusion

3,4-DGE could not be detected in plasma from either PD patients or rats during dialysis. This is presumably due to its high reactivity. 3-DG may, on the other hand, pass through the membrane and be detected in the blood.

How to Avoid Glucose Degradation Products in Peritoneal Dialysis Fluids

Objective

The formation of glucose degradation products (GDPs) during sterilization of peritoneal dialysis fluids (PDFs) is one of the most important aspects of biocompatibility of glucose-containing PDFs. Producers of PDFs are thus trying to minimize the level of GDPs in their products. 3,4-Dideoxyglucosone-3-ene (3,4-DGE) has been identified as the most bioreactive GDP in PDFs. It exists in a temperature-dependent equilibrium with a pool of 3-deoxyglucosone (3-DG) and is a precursor in the irreversible formation of 5-hydroxymethyl furaldehyde (5-HMF). The aim of the present study was to investigate how to minimize GDPs in PDFs and how different manufacturers have succeeded in doing so.

Design

Glucose solutions at different pHs and concentrations were heat sterilized and 3-DG, 3,4-DGE, 5-HMF, formaldehyde, and acetaldehyde were analyzed. Conventional as well as biocompatible fluids from different manufacturers were analyzed in parallel for GDP concentrations.

Results

The concentrations of 3-DG and 3,4-DGE produced during heat sterilization decreased when pH was reduced to about 2. Concentration of 5-HMF decreased when pH was reduced to 2.6. After further decrease to a pH of 2.0, concentration of 5-HMF increased slightly, and below a pH of 2.0 it increased considerably, together with formaldehyde; 3-DG continued to drop and 3,4-DGE remained constant. Inhibition of cell growth was paralleled by 3,4-DGE concentration at pH 2.0 – 6.0. A high glucose concentration lowered concentrations of 3,4-DGE and 3-DG at pH 5.5 and of 5-HMF at pH 1. At pH 2.2 and 3.2, glucose concentration had a minor effect on the formation of GDPs. All conventional PDFs contained high levels of 3,4-DGE and 3-DG. Concentrations were considerably lower in the biocompatible fluids. However, the concentration of 5-HMF was slightly higher in all the biocompatible fluids.

Conclusion

The best way to avoid reactive GDPs is to have a pH between 2.0 and 2.6 during sterilization. If pHs outside this range are used, it becomes more important to have high glucose concentration during the sterilization process. There are large variations in GDPs, both within and between biocompatible and conventionally manufactured PDFs.

Peritoneal Injury by Methylglyoxal in Peritoneal Dialysis

Background

Peritoneal dialysis (PD) is a common treatment for patients with reduced or absent renal function. Long-term PD leads to peritoneal injury with structural changes and functional decline, such as ultrafiltration loss. At worst, peritoneal injury leads to encapsulating peritoneal sclerosis, a serious complication of PD. Glucose degradation products contained in PD fluids contribute to the bioincompatibility of conventional PD fluids. Methylglyoxal (MGO) is an extremely toxic glucose degradation product. The present study examined the injurious effect of MGO on peritoneum in vivo.

Methods

Male Sprague–Dawley rats ( n = 6) were administered PD fluids (pH 5.0) containing 0, 0.66, 2, 6.6, or 20 mmol/L MGO every day for 21 days. On day 22, peritoneal function was estimated by the peritoneal equilibration test. Drained dialysate was analyzed for type IV collagen-7S, matrix metalloproteinase (MMP), and vascular endothelial growth factor (VEGF). Histological analysis was also performed.

Results

In rats receiving PD fluids containing more than 0.66 mmol/L MGO, peritoneal function decreased significantly and levels of type IV collagen-7S and MMP-2 in drained dialysate increased significantly. In the 20-mmol/L MGO-treated rats, loss of body weight, expression of VEGF, thickening of the peritoneum, and formation of abdominal cocoon were induced. MMP-2 and VEGF were produced by infiltrating cells in the peritoneum. Type IV collagen was detected in basement membrane of microvessels.

Conclusion

MGO induced not only peritoneal injury but also abdominal cocoon formation in vivo. The decline of peritoneal function may result from reconstitution of microvessel basement membrane or neovascularization.

Effects of Peritoneal Resting on Peritoneal Fluid Transport Kinetics

Background

Peritoneal resting has been used to restore peritoneal ultrafiltration capacity in peritoneal dialysis patients. Therefore, in the present study, we made a detailed investigation on the effects of peritoneal resting on peritoneal fluid transport characteristics in patients on continuous ambulatory peritoneal dialysis (CAPD).

Methods

A temporary transfer to daytime ambulatory peritoneal dialysis with a nocturnal “empty belly” was applied to let the peritoneal membrane rest overnight in patients with poor ultrafiltration capacity. All included patients were asked to record appropriately their dialysis exchanges for the assessment of peritoneal fluid transport characteristics, which were evaluated before and after peritoneal resting.

Results

Seven CAPD patients were included in the present study. There was a significant improvement in peritoneal ultrafiltration capacity as assessed by ultrafiltration volume per gram of glucose load. Patients’ daily glucose exposure and dialysate-to-plasma ratio of creatinine were significantly decreased after peritoneal resting. The peritoneal fluid absorption rate was also significantly decreased after peritoneal resting: 1.011 ± 0.4484 versus 0.625 ± 0.3833 mL/minute.

Conclusion

The present study suggests that peritoneal resting can improve CAPD patients’ ultrafiltration capacity and decrease the use of hypertonic dialysis solution. The improved ultrafiltration capacity by peritoneal resting was due to decreased membrane solute transport rate and decreased peritoneal fluid absorption rate.

Dissecting the Antimicrobial Composition of Honey

Honey is a complex sweet food stuff with well-established antimicrobial and antioxidant properties. It has been used for millennia in a variety of applications, but the most noteworthy include the treatment of surface wounds, burns and inflammation. A variety of substances in honey have been suggested as the key component to its antimicrobial potential; polyphenolic compounds, hydrogen peroxide, methylglyoxal and bee-defensin 1. These components vary greatly across honey samples due to botanical origin, geographical location and secretions from the bee. The use of medical grade honey in the treatment of surface wounds and burns has been seen to improve the healing process, reduce healing time, reduce scarring and prevent microbial contamination. Therefore, if medical grade honeys were to be included in clinical treatment, it would reduce the demand for antibiotic usage. In this review, we outline the constituents of honey and how they affect antibiotic potential in a clinical setting. By identifying the key components, we facilitate the development of an optimally antimicrobial honey by either synthetic or semisynthetic production methods.

Neuronal damage and shortening of lifespan in C. elegans by peritoneal dialysis fluid: Protection by glyoxalase-1

Glucose and glucose degradation products (GDPs), contained in peritoneal dialysis (PD) fluids, contribute to the formation of advanced glycation end-products (AGEs). Local damaging effects, resulting in functional impairment of the peritoneal membrane, are well studied. It is also supposed that detoxification of AGE precursors by glyoxalase-1 (GLO1) has beneficial effects on GDP-mediated toxicity. The aim of the current study was to analyze systemic detrimental effects of PD fluids and their prevention by glyoxlase-1. Wild-type and GLO1-overexpressing Caenorhabditis elegans (C. elegans) were cultivated in the presence of low- and high-GDP PD fluids containing 1.5 or 4% glucose. Lifespan, neuronal integrity and neuronal functions were subsequently studied. The higher concentrations of glucose and GDP content resulted in a decrease of maximum lifespan by 2 (P<0.01) and 9 days (P<0.001), respectively. Exposure to low- and high-GDP fluids caused reduction of neuronal integrity by 34 (P<0.05) and 41% (P<0.05). Cultivation of animals in the presence of low-GDP fluid containing 4% glucose caused significant impairment of neuronal function, reducing relative and absolute head motility by 58.5 (P<0.01) and 56.7% (P<0.01), respectively; and relative and absolute tail motility by 55.1 (P<0.05) and 55.0% (P<0.05), respectively. Taken together, GLO1 overexpression protected from glucose-induced lifespan reduction, neurostructural damage and neurofunctional damage under low-GDP-conditions. In conclusion, both glucose and GDP content in PD fluids have systemic impact on the lifespan and neuronal integrity of C. elegans. Detoxification of reactive metabolites by GLO1 overexpression was sufficient to protect lifespan, neuronal integrity and neuronal function in a low-GDP environment. These data emphasize the relevance of the GLO1 detoxifying pathway as a potential therapeutic target in the treatment of reactive metabolite-mediated pathologies.

Specific heparanase inhibition reverses glucose-induced mesothelial-to-mesenchymal transition

Background

Epithelial-to-mesenchymal transition (EMT) of peritoneal mesothelial cells induced by high glucose (HG) levels is a major biological mechanism leading to myofibroblast accumulation in the omentum of patients on peritoneal dialysis (PD). Heparanase (HPSE), an endoglycosidase that cleaves heparan sulfate chains, is involved in the EMT of several cell lines, and may have a major role in this pro-fibrotic process potentially responsible for the failure of dialysis. Its specific inhibition may therefore plausibly minimize this pathological condition.

Methods

An in vitro study employing several biomolecular strategies was conducted to assess the role of HPSE in the HG-induced mesothelial EMT process, and to measure the effects of its specific inhibition by SST0001, a N-acetylated glycol-split heparin with a strong anti-HPSE activity. Rat mesothelial cells were grown for 6 days in HG (200 mM) culture medium with or without SST0001. Then EMT markers (VIM, α-SMA, TGF-β) and vascular endothelial growth factor (VEGF) (a factor involved in neoangiogenesis) were measured by real-time PCR and immunofluorescence/western blotting. As a functional analysis, trans-epithelial resistance (TER) and permeability to albumin were also measured in our in vitro model using a Millicell-ERS ohmmeter and a spectrophotometer, respectively.

Results

Our results showed that 200 mM of glucose induced a significant gene and protein up-regulation of VEGF and all EMT markers after 6 days of culture. Intriguingly, adding SST0001 on day 3 reversed these biological and cellular effects. HPSE inhibition also restored the normal TER and permeability lost during the HG treatment.

Conclusion

Taken together, our data confirm that HG can induce EMT of mesothelial cells, and that HPSE plays a central part in this process. Our findings also suggest that pharmacological HPSE inhibition could prove a valuable therapeutic tool for minimizing fibrosis and avoiding a rapid decline in the efficacy of dialysis in patients on PD, though clinical studies and/or trials would be needed to confirm the clinical utility of this treatment.

"Biocompatible" Neutral pH Low-GDP Peritoneal Dialysis Solutions: Much Ado About Nothing?

Adverse outcomes in peritoneal dialysis (PD), including PD related infections, the loss of residual kidney function (RKF), and longitudinal, deleterious changes in peritoneal membrane function continue to limit the long-term success of PD therapy. The observation that these deleterious changes occur upon exposure to conventional glucose-based PD solutions fuels the search for a more biocompatible PD solution. The development of a novel PD solution with a neutral pH, and lower in glucose degradation products (GDPs) compared to its conventional predecessors has been labeled a "biocompatible" solution. While considerable evidence in support of these novel solutions' biocompatibility has emerged from cell culture and animal studies, the clinical benefits as compared to conventional PD solutions are less clear. Neutral pH low GDP (NpHLGDP) PD solutions appear to be effective in reducing infusion pain, but their effects on other clinical endpoints including peritoneal membrane function, preservation of RKF, PD-related infections, and technique and patient survival are less clear. The literature is limited by studies characterized by relatively few patients, short follow-up time, heterogeneity with regards to the novel PD solution type under study, and the different patient populations under study. Nonetheless, the search for a more biocompatible PD solution continues with emerging data on promising non glucose-based solutions.

Feasibility of Mesothelial Transplantation during Experimental Peritoneal Dialysis and Peritonitis

The mesothelial cell layer lining the peritoneum orchestrates peritoneal homeostasis. Continuous exposure to peritoneal dialysis fluids and episodes of peritonitis may damage the monolayer irreversibly, eventually leading to adhesion formation and fibrosis/sclerosis of the peritoneum. Autologous mesothelial cell transplantation is thought to be one of the options to reduce dysfunction of the peritoneal membrane. In this article we will review the mesothelial cell transplantation experiments performed in the field of peritoneal dialysis and peritonitis. In addition we will focus on the trouble shooting using cultured autologous mesothelial cells for transplantation.

Maillard Proteomics: Opening New Pages

Protein glycation is a ubiquitous non-enzymatic post-translational modification, formed by reaction of protein amino and guanidino groups with carbonyl compounds, presumably reducing sugars and α-dicarbonyls. Resulting advanced glycation end products (AGEs) represent a highly heterogeneous group of compounds, deleterious in mammals due to their pro-inflammatory effect, and impact in pathogenesis of diabetes mellitus, Alzheimer's disease and ageing. The body of information on the mechanisms and pathways of AGE formation, acquired during the last decades, clearly indicates a certain site-specificity of glycation. It makes characterization of individual glycation sites a critical pre-requisite for understanding in vivo mechanisms of AGE formation and developing adequate nutritional and therapeutic approaches to reduce it in humans. In this context, proteomics is the methodology of choice to address site-specific molecular changes related to protein glycation. Therefore, here we summarize the methods of Maillard proteomics, specifically focusing on the techniques providing comprehensive structural and quantitative characterization of glycated proteome. Further, we address the novel break-through areas, recently established in the field of Maillard research, i.e., in vitro models based on synthetic peptides, site-based diagnostics of metabolism-related diseases (e.g., diabetes mellitus), proteomics of anti-glycative defense, and dynamics of plant glycated proteome during ageing and response to environmental stress.

Nano-sized carriers in gene therapy for peritoneal fibrosis in vivo

Peritoneal fibrosis is a crucial complication in patients receiving peritoneal dialysis. It is a major pathological feature of peritoneal membrane failure, which leads to withdrawal of peritoneal dialysis. No specific therapy has yet been established for the treatment of peritoneal fibrosis. However, gene therapy may be a viable option, and various nano-sized carriers, including viral and non-viral vectors, have been shown to enhance the delivery and efficacy of gene therapy for peritoneal fibrosis in vivo. This review focuses on the use of nano-sized carriers in gene therapy of peritoneal fibrosis in vivo.

Increased Dicarbonyl Stress as a Novel Mechanism of Multi-Organ Failure in Critical Illness

Molecular pathological pathways leading to multi-organ failure in critical illness are progressively being unravelled. However, attempts to modulate these pathways have not yet improved the clinical outcome. Therefore, new targetable mechanisms should be investigated. We hypothesize that increased dicarbonyl stress is such a mechanism. Dicarbonyl stress is the accumulation of dicarbonyl metabolites (i.e., methylglyoxal, glyoxal, and 3-deoxyglucosone) that damages intracellular proteins, modifies extracellular matrix proteins, and alters plasma proteins. Increased dicarbonyl stress has been shown to impair the renal, cardiovascular, and central nervous system function, and possibly also the hepatic and respiratory function. In addition to hyperglycaemia, hypoxia and inflammation can cause increased dicarbonyl stress, and these conditions are prevalent in critical illness. Hypoxia and inflammation have been shown to drive the rapid intracellular accumulation of reactive dicarbonyls, i.e., through reduced glyoxalase-1 activity, which is the key enzyme in the dicarbonyl detoxification enzyme system. In critical illness, hypoxia and inflammation, with or without hyperglycaemia, could thus increase dicarbonyl stress in a way that might contribute to multi-organ failure. Thus, we hypothesize that increased dicarbonyl stress in critical illness, such as sepsis and major trauma, contributes to the development of multi-organ failure. This mechanism has the potential for new therapeutic intervention in critical care.

Chemistry and clinical relevance of carbohydrate degradation in drugs

Carbohydrate degradation products are formed during heat sterilization in drugs containing (poly-)glucose as osmotic agents. Given this situation, peritoneal dialysis fluids (PDFs) and infusion fluids are of particular clinical relevance, because these drugs deliver process contaminants either over a longer period or directly into the circulation of patients who are critically ill. For the development of suitable mitigation strategies, it is important to understand the reaction mechanisms of carbohydrate degradation during sterilization and how the resulting products interact with physiological targets at the molecular level. Furthermore, reliable, comprehensive, and highly sensitive quantification methods are required for product control and toxicological evaluation.

Impact of a low-glucose peritoneal dialysis regimen on fibrosis and inflammation biomarkers

BACKGROUND

The impact of a low-glucose peritoneal dialysis (PD) regimen on biomarkers of peritoneal inflammation, fibrosis and membrane integrity remains to be investigated.

METHODS

In a randomized, prospective study, 80 incident PD patients received either a low-glucose regimen comprising Physioneal (P), Extraneal (E) and Nutrineal (N) (Baxter Healthcare Corporation, Deerfield, IL, USA) (PEN group), or Dianeal (control group) for 12 months, after which both groups continued with Dianeal dialysis for 6 months. Serum and dialysate levels of vascular endothelial growth factor (VEGF), decorin, hepatocyte growth factor (HGF), interleukin-6 (IL-6), macrophage migration inhibitory factor (MIF), hyaluronan (HA), adiponectin, soluble-intracellular adhesion molecule (s-ICAM), vascular cell adhesion molecule-1 (VCAM-1) and P-selectin, and dialysate cancer antigen 125 (CA125), were measured after 12 and 18 months. This paper focuses on results after 12 months, when patients in the PEN group changed to glucose-based PD fluid (PDF).

RESULTS

At the end of 12 months, effluent dialysate levels of CA125, decorin, HGF, IL-6, adiponectin and adhesion molecules were significantly higher in the PEN group compared to controls, but all decreased after patients switched to glucose-based PDF. Macrophage migration inhibitory factor level was lower in the PEN group but increased after changing to glucose-based PDF and was similar to controls at 18 months. Serum adiponectin level was higher in the PEN group at 12 months, but was similar in the 2 groups at 18 months. Body weight, residual renal function, ultrafiltration volume and total Kt/V did not differ between both groups. Dialysate-to-plasma creatinine ratio at 4 h was higher in the PEN group at 12 months and remained so after switching to glucose-based PDF.

CONCLUSION

Changes in the biomarkers suggest that the PEN PD regimen may be associated with better preservation of peritoneal membrane integrity and reduced systemic vascular endothelial injury.

The Therapeutic Potential of Human Umbilical Mesenchymal Stem Cells From Wharton's Jelly in the Treatment of Rat Peritoneal Dialysis-Induced Fibrosis

A major complication in continuous, ambulatory peritoneal dialysis in patients with end-stage renal disease who are undergoing long-term peritoneal dialysis (PD) is peritoneal fibrosis, which can result in peritoneal structural changes and functional ultrafiltration failure. Human umbilical mesenchymal stem cells (HUMSCs) in Wharton's jelly possess stem cell properties and are easily obtained and processed. This study focuses on the effects of HUMSCs on peritoneal fibrosis in in vitro and in vivo experiments. After 24-hour treatment with mixture of Dulbecco's modified Eagle's medium and PD solution at a 1:3 ratio, primary human peritoneal mesothelial cells became susceptible to PD-induced cell death. Such cytotoxic effects were prevented by coculturing with primary HUMSCs. In a rat model, intraperitoneal injections of 20 mM methylglyoxal (MGO) in PD solution for 3 weeks (the PD/MGO 3W group) markedly induced abdominal cocoon formation, peritoneal thickening, and collagen accumulation. Immunohistochemical analyses indicated neoangiogenesis and significant increase in the numbers of ED-1- and α-smooth muscle actin (α-SMA)-positive cells in the thickened peritoneum in the PD/MGO 3W group, suggesting that PD/MGO induced an inflammatory response. Furthermore, PD/MGO treatment for 3 weeks caused functional impairments in the peritoneal membrane. However, in comparison with the PD/MGO group, intraperitoneal administration of HUMSCs into the rats significantly ameliorated the PD/MGO-induced abdominal cocoon formation, peritoneal fibrosis, inflammation, neoangiogenesis, and ultrafiltration failure. After 3 weeks of transplantation, surviving HUMSCs were found in the peritoneum in the HUMSC-grafted rats. Thus, xenografts of HUMSCs might provide a potential therapeutic strategy in the prevention of peritoneal fibrosis. Significance: This study demonstrated that direct intraperitoneal transplantation of human umbilical mesenchymal stem cells into the rat effectively prevented peritoneal dialysis/methylglyoxal-induced abdominal cocoon formation, ultrafiltration failure, and peritoneal membrane alterations such as peritoneal thickening, fibrosis, and inflammation. These findings provide a basis for a novel approach for therapeutic benefits in the treatment of encapsulating peritoneal sclerosis.

Animal Models of Peritoneal Dialysis: Thirty Years of Our Own Experience

Experimental animal models improve our understanding of technical problems in peritoneal dialysis PD, and such studies contribute to solving crucial clinical problems. We established an acute and chronic PD model in nonuremic and uremic rats. We observed that kinetics of PD in rats change as the animals are aging, and this effect is due not only to an increasing peritoneal surface area, but also to changes in the permeability of the peritoneum. Changes of the peritoneal permeability seen during chronic PD in rats are comparable to results obtained in humans treated with PD. Effluent dialysate can be drained repeatedly to measure concentration of various bioactive molecules and to correlate the results with the peritoneal permeability. Additionally we can study in in vitro conditions properties of the effluent dialysate on cultured peritoneal mesothelial cells or fibroblasts. We can evaluate acute and chronic effect of various additives to the dialysis fluid on function and permeability of the peritoneum. Results from such study are even more relevant to the clinical scenario when experiments are performed in uremic rats. Our experimental animal PD model not only helps to understand the pathophysiology of PD but also can be used for testing biocompatibility of new PD fluids.

Increased peritoneal damage in glyoxalase 1 knock-down mice treated with peritoneal dialysis

BACKGROUND

Peritoneal dialysis (PD) is limited by peritoneal fibrosis and ultrafiltration failure. This is in part caused by the high concentration of glucose degradation products (GDPs) present in PD fluids (PDF) as a consequence of heat sterilization. Existing research in long-term PD has mainly dealt with the toxicity induced by GDPs and the development of therapeutic strategies to reduce the cellular burden of GDPs. Currently, there are few data regarding the potential role of detoxification systems of GDP in PD. In this study, the role of glyoxalase 1 (Glo1), the major detoxification pathway for dicarbonyl-derived GD such as methylglyoxal (MG) and glyoxal (Gx), was investigated in vivo using heterozygous knock-down mice for Glo1 (Glo1(-/+)).

METHODS

Wild-type (WT) and Glo1(-/+) mice were repeatedly treated with PDF containing low and high amounts of GDP, particularly with respect to the content of dicarbonyls. After 12 weeks of treatment with PDF, peritoneal damage and function were evaluated.

RESULTS

Glo1(-/+) mice treated with PDF showed increased formation of advanced glycation endproduct (AGE) when compared with WT mice, particularly the Gx-derived AGE, carboxymethyl-lysine. This was associated with increased inflammation, neovascularization, increased peritoneal fibrosis and impaired peritoneal function.

CONCLUSIONS

This study suggests a pivotal and underestimated role for Glo1 as a detoxifying enzyme in GDP-associated peritoneal toxicity in PD. The indirect and direct modulation of Glo1 may therefore offer a new therapeutic option in prevention of GDP-induced peritoneal damage in PD.

Extending the spectrum of α-dicarbonyl compounds in vivo

Maillard α-dicarbonyl compounds are known as central intermediates in advanced glycation end product (AGE) formation. Glucose is the primary source of energy for the human body, whereas l-threo-ascorbic acid (vitamin C) is an essential nutrient, involved in a variety of enzymatic reactions. Thus, the Maillard degradation of glucose and ascorbic acid is of major importance in vivo. To understand the complex mechanistic pathways of AGE formation, it is crucial to extend the knowledge on plasma concentrations of reactive key α-dicarbonyl compounds (e.g. 1-deoxyglucosone). With the present work, we introduce a highly sensitive LC-MS/MS multimethod for human blood plasma based on derivatization with o-phenylenediamine under acidic conditions. The impact of workup and reaction conditions, particularly of pH, was thoroughly evaluated. A comprehensive validation provided the limit of detection, limit of quantitation, coefficients of variation, and recovery rates. The method includes the α-dicarbonyls 1-deoxyglucosone, 3-deoxyglucosone, glucosone, Lederer's glucosone, dehydroascorbic acid, 2,3-diketogulonic acid, 1-deoxypentosone, 3-deoxypentosone, 3,4-dideoxypentosone, pentosone, 1-deoxythreosone, 3-deoxythreosone, threosone, methylglyoxal, glyoxal; the α-keto-carboxylic acids pyruvic acid and glyoxylic acid; and the dicarboxylic acid oxalic acid. The method was then applied to the analyses of 15 healthy subjects and 24 uremic patients undergoing hemodialysis. The comparison of the results revealed a clear shift in the product spectrum. In most cases, the plasma levels of target analytes were significantly higher. Thus, this is the first time that a complete spectrum of α-dicarbonyl compounds relevant in vivo has been established. The results provide further insights into the chemistry of AGE formation and will be helpful to find specific markers to differentiate between the various precursors of glycation.

Structure- and concentration-specific assessment of the physiological reactivity of α-dicarbonyl glucose degradation products in peritoneal dialysis fluids

In peritoneal dialysis (PD), glucose degradation products (GDPs), which are formed during heat sterilization of dialysis fluids, lead to structural and functional changes in the peritoneal membrane, which eventually result in the loss of its ultrafiltration capacity. To determine the molecular mechanisms behind these processes, the present study tested the influence of the six major α-dicarbonyl GDPs in PD fluids, namely, glyoxal, methylglyoxal, 3-deoxyglucosone (3-DG), 3-deoxygalactosone (3-DGal), 3,4-dideoxyglucosone-3-ene (3,4-DGE), and glucosone with respect to their potential to impair the enzymatic activity of RNase A as well as their effects on cell viability. For comprehensive risk assessment, the α-dicarbonyl GDPs were applied separately and in concentrations as present in conventional PD fluids. Thus, it was shown that after 5 days, glucosone impaired RNase A activity most distinctly (58% remaining activity, p < 0.001 compared to that of the control), followed by 3,4-DGE (62%, p < 0.001), 3-DGal (66%, p < 0.001), and 3-DG (76%, p < 0.01). Methylglyoxal and glyoxal caused weaker inactivation with significant effects only after 10 days of incubation (79%, 81%, p < 0.001). Profiling of the advanced glycation end products formed during the incubation of RNase A with methylglyoxal revealed predominant formation of the arginine modifications imidazolinone, CEA/dihydroxyimidazoline, and tetrahydropyrimidine at Arg10, Arg33, Arg39, and Arg85. Particularly, modification at Arg39 may severely affect the active site of the enzyme. Additionally, structure- and concentration-specific assessment of the cytotoxicity of the α-dicarbonyl GDPs was performed. Although present at very low concentration, the cytotoxic effect of PD fluids after 2 days of incubation was exclusively caused by 3,4-DGE (14% cell viability, p < 0.001). After 4 days of incubation, 3-DGal (13% cell viability, p < 0.001), 3-DG (24%, p < 0.001), and, to a lower extent, glyoxal and methylglyoxal (both 57%, p < 0.01) also reduced cell viability significantly. In conclusion, 3,4-DGE, 3-DGal, and glucosone appear to be the most relevant parameters for the biocompatibility of PD fluids.

Milieu dependence of isomeric composition of D-arabino-hexo-2-ulose in aqueous solution determined by high-resolution NMR spectroscopy

In this study, high-resolution (1)H NMR spectroscopy (600.03 MHz) and (13)C NMR spectroscopy (150.89 MHz) were used to elucidate the structures of equilibrating d-arabino-hexo-2-ulose (GLUC) (1) isomers in aqueous solution. Four isomers were formed from the investigated ketohexose, and their equilibrium is dependent on the pH value and temperature. Only hydrated GLUC (1) isomers were identified. The (2)C5-β-2,6-pyranoid and the β-2,5-furanoid GLUC (1) isomer were exclusively formed in aqueous solution. Thus, (4)C1-1,5-pyranoid isomers are predominating in the crystalline state. An increase in solution pH or temperature led to a pairwise conversion of configurative information. Thus, changing the measurement conditions permits control over the equilibrium's characteristic. Furthermore, all GLUC (1) isomers showed comparable reaction behavior regarding pH- and temperature-dependent degradation reactions.