Development and validation of an HPLC method to quantify 3,4-dideoxyglucosone-3-ene in peritoneal dialysis fluids

A Robust HPLC Approach for Quantitation of Camptothecin in Mesoporous Silica Nanoparticles Matrix and in the Presence of Its Degradation Products

BACKGROUND

Camptothecin is a potent anticancer drug used for the treatment of various cancers.

OBJECTIVE

The goal of this research investigation was to develop and validate a new stability-indicating HPLC technique for the quantitative assessment of camptothecin in in-house developed mesoporous silica nanoparticles, a novel nanoformulation matrix for the treatment of cancer.

METHOD

The Waters Inertsil® HPLC column (C18) was used for the chromatographic separation, with a flow rate of 1 mL/min, a column oven temperature of 40°C, an injection volume of 10 µL, a detection wavelength of 216 nm, and a 10 min runtime overall. An isocratic blend of phosphate buffer (10 mM, pH7.0) and acetonitrile (60:40, v/v) served as the mobile phase. Various stress conditions including acid, alkali, oxidative, photolytic, thermal, and humidity environments were tested for the quantitative estimation of the camptothecin through the proposed method.

RESULTS

The results demonstrated that the proposed method is specific (peak purity ≥0.999), accurate (99.69-100.64% w/w), precise (RSD, % <2.0), and sensitive (LOD-0.17 µg and LOQ-0.56 µg) in accordance with ICH guideline Q2 (R1). Any unidentified degradation products did not interfere with the drug's estimation. Furthermore, the current method of analysis has eliminated any excipient interference from the matrix effect caused by the numerous excipients of the formulation matrix.

CONCLUSIONS

To quantify camptothecin for routine assay purposes, this research work offers a novel and straightforward HPLC methodology with optimized chromatographic parameters, contributing to the research and development community while ensuring an appropriate and efficient use of the drug through a variety of nanoformulation for cancer treatment.

HIGHLIGHTS

The stability-indicating HPLC method was found to be specific and suitable for routine analysis of camptothecin. The absence of any interference from excipients was confirmed by forced degradation studies.

Degradation and de novo formation of nine major glucose degradation products during storage of peritoneal dialysis fluids

Reactive glucose degradation products (GDPs) are formed during heat sterilization of glucose-containing peritoneal dialysis fluids (PDFs) and may induce adverse clinical effects. Long periods of storage and/or transport of PDFs before use may lead to de novo formation or degradation of GDPs. Therefore, the present study quantified the GDP profiles of single- and double-chamber PDFs during storage. Glucosone, 3-deoxyglucosone (3-DG), 3-deoxygalactosone (3-DGal), 3,4-dideoxyglucosone-3-ene (3,4-DGE), glyoxal, methylglyoxal (MGO), acetaldehyde, formaldehyde, and 5-hydroxymethylfurfural (5-HMF) were quantified by two validated UHPLC-DAD methods after derivatization with o-phenylenediamine (dicarbonyls) or 2,4-dinitrophenylhydrazine (monocarbonyls). The PDFs were stored at 50 °C for 0, 1, 2, 4, 13, and 26 weeks. The total GDP concentration of single-chamber PDFs did not change considerably during storage (496.6 ± 16.0 µM, 0 weeks; 519.1 ± 13.1 µM, 26 weeks), but individual GDPs were affected differently. 3-DG (− 82.6 µM) and 3-DGal (− 71.3 µM) were degraded, whereas 5-HMF (+ 161.7 µM), glyoxal (+ 32.2 µM), and formaldehyde (+ 12.4 µM) accumulated between 0 and 26 weeks. Acetaldehyde, glucosone, MGO, and 3,4-DGE showed time-dependent formation and degradation. The GDP concentrations in double-chamber fluids were generally lower and differently affected by storage. In conclusion, the changes of GDP concentrations during storage should be considered for the evaluation of clinical effects of PDFs.

Effect of Processing of Whey Protein Ingredient on Maillard Reactions and Protein Structural Changes in Powdered Infant Formula

The most widely used whey protein ingredient in an infant formula (IF) is the whey protein concentrate (WPC). The processing steps used in the manufacturing of both a powdered IF and a WPC introduce protein modifications that may decrease the nutritional quality. A gently processed whey protein ingredient (serum protein concentrate; SPC) was manufactured and used for the production of a powdered IF. The SPC and the SPC-based IF were compared to the WPC and the powdered WPC-based IF. Structural protein modifications were evaluated, and Maillard reaction products, covering furosine, α-dicarbonyls, furans, and advanced glycation end products, were quantified in the IFs and their protein ingredients. IF processing was responsible for higher levels of protein modifications compared to the levels observed in the SPC and WPC. Furosine levels and aggregation were most pronounced in the WPC, but the SPC contained a high level of methylglyoxal, revealing that other processing factors should be considered in addition to thermal processing.

Quantification of Degradation Products Formed during Heat Sterilization of Glucose Solutions by LC-MS/MS: Impact of Autoclaving Temperature and Duration on Degradation

Heat sterilization of glucose solutions can lead to the formation of various glucose degradation products (GDPs) due to oxidation, hydrolysis, and dehydration. GDPs can have toxic effects after parenteral administration due to their high reactivity. In this study, the application of the F0 concept to modify specific time/temperature models during heat sterilization and their influence on the formation of GDPs in parenteral glucose solutions was investigated using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). Glucose solutions (10%, w/v) were autoclaved at 111 °C, 116 °C, and 121 °C for different durations. The GDPs glyoxal, methylglyoxal, glucosone, 3-deoxyglucosone/3-deoxygalactosone, 3,4-dideoxyglucosone-3-ene, and 5-hydroxymethylfurfural were quantified after derivatization with o-phenylenediamine by an optimized LC-MS/MS method. For all GDPs, the limit of detection was <0.078 μg/mL, and the limit of quantification was <0.236 μg/mL. The autoclaving time of 121 °C and 15 min resulted in the lowest levels of 3-DG/3-DGal and 5-HMF, but in the highest levels of GO and 2-KDG. The proposed LC-MS/MS method is rapid and sensitive. So far, only 5-HMF concentrations are limited by the regulatory authorities. Our results suggest reconsidering the impurity limits of various GDPs, especially the more toxic ones such as GO and MGO, by the Pharmacopoeias.

Glucose Derivative Induced Vasculopathy in Children on Chronic Peritoneal Dialysis

[Figure: see text].

Identification and quantification of glucose degradation products in heat-sterilized glucose solutions for parenteral use by thin-layer chromatography

During heat sterilization of glucose solutions, a variety of glucose degradation products (GDPs) may be formed. GDPs can cause cytotoxic effects after parenteral administration of these solutions. The aim of the current study therefore was to develop a simple and quick high-performance thin-layer chromatography (HPTLC) method by which the major GDPs can be identified and (summarily) quantified in glucose solutions for parenteral administration. All GDPs were derivatized with o-phenylenediamine (OPD). The resulting GDP derivatives (quinoxalines) were applied to an HPTLC plate. After 20 minutes of chamber saturation with the solvent, the HPTLC plate was developed in a mixture of 1,4-dioxane-toluene-glacial acetic acid (49:49:2, v/v/v), treated with thymol-sulfuric acid spray reagent, and heated at 130°C for 10 minutes. Finally, the GDPs were quantified by using a TLC scanner. For validation, the identities of the quinoxaline derivatives were confirmed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Glyoxal (GO)/methylglyoxal (MGO) and 3-deoxyglucosone (3-DG)/3-deoxygalactosone (3-DGal) could be identified and quantified in pairs, glucosone (2-KDG), 5-hydroxymethylfurfural (5-HMF), and 3,4-dideoxyglucosone-3-ene (3,4-DGE) each individually. For 2-KDG, the linearity of the method was demonstrated in the range of 1–50 μg/mL, for 5-HMF and 3,4-DGE 1–75 μg/mL, for GO/MGO 2–150 μg/mL, and for 3-DG/3-DGal 10–150 μg/mL. All GDPs achieved a limit of detection (LOD) of 2 μg/mL or less and a limit of quantification (LOQ) of 10 μg/mL or less. R² was 0.982 for 3.4-DGE, 0.997 for 5-HMF, and 0.999 for 2-KDG, 3-DG/3-DGal, and GO/MGO. The intraday precision was between 0.4 and 14.2% and the accuracy, reported as % recovery, between 86.4 and 112.7%. The proposed HPTLC method appears to be an inexpensive, fast, and sufficiently sensitive approach for routine quantitative analysis of GDPs in heat-sterilized glucose solutions.

Identification of [6-Hydroxy-2-(hydroxymethyl)-5-oxo-5,6-dihydro-2 H-pyran-3-yl]-cysteine (HHPC) as a Cysteine-specific Modification Formed from 3,4-Dideoxyglucosone-3-ene (3,4-DGE)

Glucose degradation products (GDPs) are formed from glucose and other reducing sugars during heat treatment, for example, in heat-sterilized peritoneal dialysis fluids or foods. Because of their reactive mono- and dicarbonyl structure, they react readily with proteins, resulting in the formation of advanced glycation end products (AGEs), loss of protein functionality, and cytotoxicity. Among the GDPs, 3,4-dideoxyglucosone-3-ene (3,4-DGE) exerts the strongest effects despite its relatively low concentration levels. The goal of the present study was therefore to identify the structure of specific protein modifications deriving from 3,4-DGE. A nonapeptide containing the reactive amino acids lysine, arginine, and cysteine was incubated with 3,4-DGE and the dominant GDPs 3-deoxyglucosone (3-DG) and 3-deoxygalactosone (3-DGal) in concentrations as present in peritoneal dialysis fluids (235 μM 3-DG, 100 μM 3-Gal, and 11 μM 3,4-DGE). Glycation rate and product formation were determined by ultra-HPLC-MS/MS (UHPLC-MS/MS). 3,4-DGE showed the strongest glycation activity. After 2 h of incubation, 3,4-DGE had modified 57% of the nonapeptide, whereas 3-DG had modified only 2% and 3-DGal had modified 29% of the peptide. A stable 3,4-DGE-derived cysteine modification was isolated. Its structure was determined by comprehensive NMR and MS experiments to be [6-hydroxy-2-(hydroxymethyl)-5-oxo-5,6-dihydro-2 H-pyran-3-yl]-cysteine (HHPC), which represents a novel cysteine-AGE derived from 3,4-DGE. The results indicate that 3,4-DGE might contribute to a severe loss of protein functionality by forming cysteine-specific AGEs, such as HHPC.

Complement Activation in Peritoneal Dialysis-Induced Arteriolopathy

Cardiovascular disease (CVD) is the leading cause of increased mortality in patients with CKD and is further aggravated by peritoneal dialysis (PD). Children are devoid of preexisting CVD and provide unique insight into specific uremia- and PD-induced pathomechanisms of CVD. We obtained peritoneal specimens from children with stage 5 CKD at time of PD catheter insertion (CKD5 group), children with established PD (PD group), and age-matched nonuremic controls (n=6/group). We microdissected omental arterioles from tissue layers not directly exposed to PD fluid and used adjacent sections of four arterioles per patient for transcriptomic and proteomic analyses. Findings were validated in omental and parietal arterioles from independent pediatric control (n=5), CKD5 (n=15), and PD (n=15) cohorts. Transcriptomic analysis revealed differential gene expression in control versus CKD5 arterioles and in CKD5 versus PD arterioles. Gene ontology analyses revealed activation of metabolic processes in CKD5 arterioles and of inflammatory, immunologic, and stress-response cascades in PD arterioles. PD arterioles exhibited particular upregulation of the complement system and respective regulatory pathways, with concordant findings at the proteomic level. In the validation cohorts, PD specimens had the highest abundance of omental and parietal arteriolar C1q, C3d, terminal complement complex, and phosphorylated SMAD2/3, a downstream effector of TGF-β Furthermore, in the PD parietal arterioles, C1q and terminal complement complex abundance correlated with the level of dialytic glucose exposure, abundance of phosphorylated SMAD2/3, and degree of vasculopathy. We conclude that PD fluids activate arteriolar complement and TGF-β signaling, which quantitatively correlate with the severity of arteriolar vasculopathy.

Factors Generating Glucose Degradation Products In Sterile Glucose Solutions For Infusion: Statistical Relevance Determination Of Their Impacts

Sterilising glucose solutions by heat promotes the generation of a large number of glucose degradation products (GDPs). It has been shown that high levels of GDPs may result in Advanced Glycation End products that have an impact on cellular homeostasis and health in general. If data is available for peritoneal dialysis solutions, little has been published for glucose infusion fluids. It is essential to identify the parameters causing the formation of GDPs and so limit the risk of exposing patients to them. After quantifying both 5-hydroxymethyl-2-furfural, considered as an important indicator of degradation, and 2-furaldehyde, an ultimate GDP of one degradation pathway, in marketed solutions, the aim of this work is to build a model integrating all the parameters involved in the formation rates of these two GDPs: supplier, glucose amount, container material, oxygen permeability coefficient and time-lapse since manufacture. Our results show a good logarithmic relationship between GDP formation rates and time-lapse since manufacture for both GDPs. The amount of GDPs in the glucose solutions for infusion depends on the initial glucose amount, the polymer of the container, the time elapsed since manufacturing and the supplier.

Anthocyanins in different Citrus species: an UHPLC-PDA-ESI/MSn -assisted qualitative and quantitative investigation

BACKGROUND

Anthocyanins are water-soluble pigments belonging to the flavonoid family. They are typically present in the flesh and peel in the blood orange cultivars. Although blood orange young shoots and flowers are not anthocyanin-colored, lemon, citron, rangpur lime, and Meyer lemon young shoots and flowers exhibit marked pigmentation as a result of anthocyanins, demonstrating that anthocyanin biosynthesis in the Citrus genus is both tissue- and genotype-dependent. The present study aimed to examine the qualitative and quantitative anthocyanin profile of fruit and other tissues from different Citrus species.

RESULTS

The presence of anthocyanin-pigmented stigmas in the young flowers of a blood orange tree (cv. 'Moro') was characterized and reported for the first time. The dominant pigments in blood orange fruits were cyanidin 3-glucoside and cyanidin 3-(6''-malonyl-glucoside), whereas different patterns were observed in the young shoots, flowers and peel tissues of different Citrus species.

CONCLUSION

The present study is the first to report differentially expressed anthocyanin pigmentation patterns in different organs from several species of the genus Citrus. The results obtained could also represent a starting point for further investigations that aim to better understand which regulatory genes are involved in anthocyanin biosynthesis in the fruits, shoots and floral tissues of different Citrus species. © 2016 Society of Chemical Industry.

Screening of the anthocyanin profile and in vitro pancreatic lipase inhibition by anthocyanin-containing extracts of fruits, vegetables, legumes and cereals

BACKGROUND

The phytotherapic treatment of overweight and/or moderate obesity is growing widely, thus there is a great interest towards the phenolic compounds of fruits and vegetables which may inhibit pancreatic lipase enzyme. In this study, we report the chemical composition and in vitro pancreatic lipase inhibitory activity of 13 freeze-dried anthocyanin-containing extracts of different Mediterranean plants: fruits (blood orange, pomegranate, blackberry, mulberry and sumac), citrus by-products (blood orange peel), citrus vegetative tissues (young lemon shoots); vegetables (red cabbage and violet cauliflower), legume seeds (black bean), cereals (black rice), and cereal processing by-products (black rice hull). Total phenols and anthocyanins were determined. Individual anthocyanins were identified by UHPLC-PDA-ESI/MSⁿ .

RESULTS

Results revealed a wide variation in the distribution of anthocyanin compounds. Blood orange and pomegranate juice extracts had the highest total anthocyanin content and exhibited the strongest inhibition of pancreatic lipase in vitro.

CONCLUSION

Inhibitory activity was positively correlated with anthocyanin content. In appropriate formulations, anthocyanin-containing extracts could find a use as anti-obesity agents. © 2016 Society of Chemical Industry.

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.

Occurrence of (Z)-3,4-Dideoxyglucoson-3-ene in Different Types of Beer and Malt Beer as a Result of 3-Deoxyhexosone Interconversion

In beer, 3-deoxyglucosone (3-DG) and 3-deoxygalactosone (3-DGal) are important sugar degradation products, but little is known about the relevance of the interconversion reaction between these compounds in different types of beer. In the present study, 3-DG was quantitated at concentrations of 12.9-52.7 mg/L and 3-DGal at concentrations of 6.0-26.4 mg/L in different types of beer (pilsner, wheat, bock, dark, and alcohol-free beers). The concentrations in malt beer tended to be higher. Largely overlapping concentration ranges precluded a classification of beers by their 3-deoxyglycosone contents. 3,4-Dideoxyglucoson-3-ene (3,4-DGE) was identified as an important intermediate and quantitated in beer and malt beer for the first time. The E and Z isomers of the corresponding quinoxaline were synthesized by a new synthetic approach and isolated by semipreparative HPLC. An assay was developed for quantitation of (E)- and (Z)-3,4-DGE by HPLC-MS/MS, and the Z isomer was determined at concentrations of 0.3-1.7 mg/L in beer and 0.5-4.8 mg/L in malt beer samples. The E isomer was shown to be of little importance. Concentrations of 5-hydroxymethylfurfural (HMF) were twice as high as those of (Z)-3,4-DGE in beer samples (0.4-3.7 mg/L) but much higher in malt beer samples (1.6-336 mg/L).

Interference of peritoneal dialysis fluids with cell cycle mechanisms

INTRODUCTION

Peritoneal dialysis fluids (PDF) differ with respect to osmotic and buffer compound, and pH and glucose degradation products (GDP) content. The impact on peritoneal membrane integrity is still insufficiently described. We assessed global genomic effects of PDF in primary human peritoneal mesothelial cells (PMC) by whole genome analyses, quantitative real-time polymerase chain reaction (RT-PCR) and functional measurements.

METHODS

PMC isolated from omentum of non-uremic patients were incubated with conventional single chamber PDF (CPDF), lactate- (LPDF), bicarbonate- (BPDF) and bicarbonate/lactate-buffered double-chamber PDF (BLPDF), icodextrin (IPDF) and amino acid PDF (APDF), diluted 1:1 with medium. Affymetrix GeneChip U133Plus2.0 (Affymetrix, CA, USA) and quantitative RT-PCR were applied; cell viability was assessed by proliferation assays.

RESULTS

The number of differentially expressed genes compared to medium was 464 with APDF, 208 with CPDF, 169 with IPDF, 71 with LPDF, 45 with BPDF and 42 with BLPDF. Out of these genes 74%, 73%, 79%, 72%, 47% and 57% were downregulated. Gene Ontology (GO) term annotations mainly revealed associations with cell cycle (p = 10(-35)), cell division, mitosis, and DNA replication. One hundred and eighteen out of 249 probe sets detecting genes involved in cell cycle/division were suppressed, with APDF-treated PMC being affected the most regarding absolute number and degree, followed by CPDF and IPDF. Bicarbonate-containing PDF and BLPDF-treated PMC were affected the least. Quantitative RT-PCR measurements confirmed microarray findings for key cell cycle genes (CDK1/CCNB1/CCNE2/AURKA/KIF11/KIF14). Suppression was lowest for BPDF and BLPDF, they upregulated CCNE2 and SMC4. All PDF upregulated 3 out of 4 assessed cell cycle repressors (p53/BAX/p21). Cell viability scores confirmed gene expression results, being 79% of medium for LPDF, 101% for BLPDF, 51% for CPDF and 23% for IPDF. Amino acid-containing PDF (84%) incubated cells were as viable as BPDF (86%).

CONCLUSION

In conclusion, PD solutions substantially differ with regard to their gene regulating profile and impact on vital functions of PMC, i.e. on cells known to be essential for peritoneal membrane homeostasis.

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.

Effect of the dialysis fluid buffer on peritoneal membrane function in children

BACKGROUND AND OBJECTIVES

Double-chamber peritoneal dialysis fluids exert less toxicity by their neutral pH and reduced glucose degradation product content. The role of the buffer compound (lactate and bicarbonate) has not been defined in humans.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A multicenter randomized controlled trial in 37 children on automated peritoneal dialysis was performed. After a 2-month run-in period with conventional peritoneal dialysis fluids, patients were randomized to neutral-pH, low-glucose degradation product peritoneal dialysis fluids with 35 mM lactate or 34 mM bicarbonate content. Clinical and biochemical monitoring was performed monthly, and peritoneal equilibration tests and 24-hour clearance studies were performed at 0, 3, 6, and 10 months.

RESULTS

No statistically significant difference in capillary blood pH, serum bicarbonate, or oral buffer supplementation emerged during the study. At baseline, peritoneal solute equilibration and clearance rates were similar. During the study, 4-hour dialysis to plasma ratio of creatinine tended to increase, and 24-hour dialytic creatinine and phosphate clearance increased with lactate peritoneal dialysis fluid but not with bicarbonate peritoneal dialysis fluid. Daily net ultrafiltration, which was similar at baseline (lactate fluid=5.4±2.6 ml/g glucose exposure, bicarbonate fluid=4.9±1.9 ml/g glucose exposure), decreased to 4.6±1.0 ml/g glucose exposure in the lactate peritoneal dialysis fluid group, whereas it increased to 5.1±1.7 ml/g glucose exposure in the bicarbonate content peritoneal dialysis fluid group (P=0.006 for interaction).

CONCLUSIONS

When using biocompatible peritoneal dialysis fluids, equally good acidosis control is achieved with lactate and bicarbonate buffers. Improved long-term preservation of peritoneal membrane function may, however, be achieved with bicarbonate-based peritoneal dialysis fluids.

Buffer-dependent regulation of aquaporin-1 expression and function in human peritoneal mesothelial cells

BACKGROUND

Biocompatible peritoneal dialysis fluids (PDF) are buffered with lactate and/or bicarbonate. We hypothesized that the reduced toxicity of the biocompatible solutions might unmask specific effects of the buffer type on mesothelial cell functions.

METHODS

Human peritoneal mesothelial cells (HPMC) were incubated with bicarbonate (B-)PDF or lactate-buffered (L-)PDF followed by messenger RNA (mRNA) and protein analysis. Gene silencing was achieved using small interfering RNA (siRNA), functional studies using Transwell culture systems, and monolayer wound-healing assays.

RESULTS

Incubation with B-PDF increased HPMC migration in the Transwell and monolayer wound-healing assay to 245 ± 99 and 137 ± 11% compared with L-PDF. Gene silencing showed this effect to be entirely dependent on the expression of aquaporin-1 (AQP-1) and independent of AQP-3. Exposure of HPMC to B-PDF increased AQP-1 mRNA and protein abundance to 209  ± 80 and 197  ±  60% of medium control; the effect was pH dependent. L-PDF reduced AQP-1 mRNA. Addition of bicarbonate to L-PDF increased AQP-1 abundance by threefold; mRNA half-life remained unchanged. Immunocytochemistry confirmed opposite changes of AQP-1 cell-membrane abundance with B-PDF and L-PDF.

CONCLUSIONS

Peritoneal mesothelial AQP-1 abundance and migration capacity is regulated by pH and buffer agents used in PD solutions. In vivo studies are required to delineate the impact with respect to long-term peritoneal membrane integrity and function.

Chemical and physiological relevance of glucose degradation products in peritoneal dialysis

Fibrosis and vascular sclerosis are main complications that limit the long-term application of peritoneal dialysis (PD). Low biocompatibility has been largely attributed to the presence of glucose degradation products (GDPs), which are formed during the heat sterilization of PD fluids. GDPs readily modify proteins in the peritoneum, leading to a decline of their biological function. After absorption, GDPs can also promote systemic protein glycation. Additionally, GDPs may augment DNA glycation, a process enhanced in uremia. Apart from their glycating activity, GDPs induce cytotoxicity and interfere with cell signaling in peritoneal mesothelial cells. Targeted screening revealed the nature of the 6 major GDPs with α-dicarbonyl structure as 3-deoxyglucosone, 3-deoxygalactosone, glucosone, glyoxal, methylglyoxal, and 3,4-dideoxyglucosone-3-ene. Valid quantification of these GDPs was achieved by ultrahigh-performance liquid chromatography/diode array detector/tandem mass spectrometry. Identification and quantification of single GDPs allow a structure-dependent risk evaluation. As a consequence, PD fluids and processes can be improved to reduce the GDP burden of patients undergoing PD.

A new neutral-pH low-GDP peritoneal dialysis fluid

BACKGROUND

Conventional peritoneal dialysis fluids (PDFs) consist of ready-to-use solutions with an acidic pH. Sterilization of these fluids is known to generate high levels of glucose degradation products (GDPs). Although several neutral-pH, low-GDP PD solutions have been developed, none are commercially available in the United States. We analyzed pH and GDPs in Delflex Neutral pH (Fresenius Medical Care North America, Waltham, MA, USA), the first neutral-pH PDF to be approved by the US Food and Drug Administration.

METHODS

We evaluated whether patients (n = 26; age range: 18 - 78 years) could properly mix the Delflex Neutral pH PDF after standardized initial training. We further analyzed the concentrations of 10 different glucose degradation products in Delflex Neutral pH PDF and compared the results with similar analyses in other commercially available biocompatible PDFs.

RESULTS

All pH measurements (n = 288) in the delivered Delflex Neutral pH solution consistently fell within the labeled range of 7.0 ± 0.4. Analysis of mixing errors showed no significant impact on the pH results. Delflex Neutral pH, Balance (Fresenius Medical Care, Bad Homburg, Germany), BicaVera (Fresenius Medical Care), and Gambrosol Trio (Gambro Lundia AB, Lund, Sweden) exhibited similar low total GDP concentrations, with maximums in the 4.25% solutions of 88 μmol/L, 74 μmol/L, 74 μmol/L, and 79 μmol/L respectively; the concentration in Physioneal (Baxter Healthcare Corporation, Deerfield, IL, USA) was considerably higher at 263.26 μmol/L. The total GDP concentration in Extraneal (Baxter Healthcare Corporation) was 63 μmol/L, being thus slightly lower than the concentrations in the 4.25% glucose solutions, but higher than the concentrations in the 1.5% and 2.5% glucose solutions.

CONCLUSIONS

The new Delflex Neutral pH PDF consistently delivers neutral pH with minimal GDPs.

Rapid and sensitive determination of the intermediates of advanced glycation end products in the human nail by ultra-performance liquid chromatography with electrospray ionization time-of-flight mass spectrometry

The resolution of the intermediate advanced glycation end products (AGEs) in the human nail was carried out by the combination of 4,5-dimethyl-1,2-phenylenediamine (DMPD) derivatives and ultra-performance liquid chromatography with electrospray ionization time-of-flight mass spectrometry (UPLC-ESI-TOF-MS). The reaction of the reagent with 3-deoxyglucosone (3-DG), methylglyoxal (MG), and glyoxal (GO) effectively proceeds at 60°C for 2h. The resulting derivatives were efficiently separated by a gradient program (a mixture of water and acetonitrile containing 0.1% formic acid) using a reversed-phase ACQUITY UPLC BEH C(18) column (1.7 μm, 50×2.1 mm i.d.) and sensitively detected by TOF-MS. The detection limits (signal-to-noise ratio=5) of the TOF-MS were 10 to 50 fmol. A good linearity was achieved from the calibration curve, which was obtained by plotting the peak area ratios of the analytes relative to the internal standard (IS) (i.e., 2,3-hexanedione) versus the injected amounts of 3-DG, MG, and GO (r(2)>0.999), and the intra- and interday assay precisions were less than 6.89%. The derivatives of the compounds in the human nail were successfully identified by the proposed procedure. As we know, these three kinds of dicarbonyl intermediates in the formation of AGEs-3-DG, MG, and GO-were first found in human nail samples. Using these methods, the amounts of compound in the nails of healthy volunteers and diabetic patients were determined. When comparing the index from the diabetic patients with that from healthy volunteers, there is no significant difference in the content of the MG and GO in the nails. However, a statistically significant (P<0.001) correlation was observed between the 3-DG concentrations. Because the proposed method provides a good mass accuracy and the trace detection of the dicarbonyl intermediates of AGEs in the human nail, this analytical technique could be a noninvasive technique to assist in the diagnosis and assessment of disease activity in diabetic patients. Here we present a novel, sensitive, and simple method for the simultaneous determination of dicarbonyl compounds in the human nail.

Quantification of the six major α-dicarbonyl contaminants in peritoneal dialysis fluids by UHPLC/DAD/MSMS

During heat sterilization of peritoneal dialysis solutions, glucose is partially transformed into glucose degradation products (GDPs), which significantly reduce the biocompatibility of these medicinal products. Targeted α-dicarbonyl screening identified glyoxal, methylglyoxal, 3-deoxyglucosone, 3,4-dideooxyglucosone-3-ene, glucosone, and 3-deoxygalactosone as the major six GDPs with α-dicarbonyl structure. In the present study, an ultra-high-performance liquid chromatography method was developed which allows the separation of all relevant α-dicarbonyl GDPs within a run time of 15 min after derivatization with o-phenylenediamine. Hyphenated diode array detection/tandem mass spectrometry detection provides very robust quantification and, at the same time, unequivocal peak confirmation. Systematic evaluation of the derivatization process resulted in an optimal derivatization period that provided maximal derivatization yield, minimal de novo formation (uncertainty range ±5%), and maximal sample throughput. The limit of detection of the method ranged from 0.13 to 0.19 μM and the limit of quantification from 0.40 to 0.57 μM. Relative standard deviations were below 5%, and recovery rates ranged between 91% and 154%, dependent on the type and concentration of the analyte (in 87 out of 90 samples, recovery rates were 100 ± 15%). The method was then applied for the analysis of commercial peritoneal dialysis fluids (nine different product types, samples from three lots of each).

Solutions for peritoneal dialysis in children: recommendations by the European Pediatric Dialysis Working Group

The purpose of this article is to provide recommendations on the choice of peritoneal dialysis (PD) fluids in children by the European Pediatric Dialysis Working Group. The literature on experimental and clinical studies with PD solutions in children and adults was analyzed together with consensus discussions within the group. A grading was performed based on the international KDIGO nomenclature and methods. The lowest glucose concentration possible should be used. Icodextrin may be applied once daily during the long dwell, in particular in children with insufficient ultrafiltration. Infants on PD are at risk of ultrafiltration-associated sodium depletion, while anuric adolescents may have water and salt overload. Hence, the sodium chloride balance needs to be closely monitored. In growing children, the calcium balance should be positive and dialysate calcium adapted according to individual needs. Limited clinical experience with amino acid-based PD fluids in children suggests good tolerability. The anabolic effect, however, is small; adequate enteral nutrition is preferred. CPD fluids with reduced glucose degradation products (GDP) content reduce local and systemic toxicity and should be preferred whenever possible. Correction of metabolic acidosis is superior with pH neutral bicarbonate-based fluids compared with single-chamber, acidic, lactate-based solutions. Prospective comparisons of low GDP solutions with different buffer compositions are still few, and firm recommendations cannot yet be given, except when hepatic lactate metabolism is severely compromised.

Peritoneal dialysis tailored to pediatric needs

Consideration of specific pediatric aspects is essential to achieve adequate peritoneal dialysis (PD) treatment in children. These are first of all the rapid growth, in particular during infancy and puberty, which must be accompanied by a positive calcium balance, and the age dependent changes in body composition. The high total body water content and the high ultrafiltration rates required in anuric infants for adequate nutrition predispose to overshooting convective sodium losses and severe hypotension. Tissue fragility and rapid increases in intraabdominal fat mass predispose to hernia and dialysate leaks. Peritoneal equilibration tests should repeatedly been performed to optimize individual dwell time. Intraperitoneal pressure measurements give an objective measure of intraperitoneal filling, which allow for an optimized dwell volume, that is, increased dialysis efficiency without increasing the risk of hernias, leaks, and retrofiltration. We present the concept of adapted PD, that is, the combination of short dwells with low fill volume to promote ultrafiltration and long dwells with a high fill volume to improve purification within one PD session. The use of PD solutions with low glucose degradation product content is recommended in children, but unfortunately still not feasible in many countries.

3-Deoxygalactosone, a new glucose degradation product in peritoneal dialysis fluids: identification, quantification by HPLC/DAD/MSMS and its pathway of formation

Heat sterilization of peritoneal dialysis (PD) fluids leads to the formation of glucose degradation products (GDPs), which considerably impair long-term application of PD. Knowledge of the exact composition of GDPs present in a PD fluid is important to improve the biocompatibility of dialysis solutions. The present study conducted a targeted screening for novel GDPs with α-dicarbonyl structure in PD fluids. Thus, 3-deoxygalactosone (3-DGal) was identified for the first time in PD fluids. Quantification of 3-DGal was achieved by high-performance liquid chromatography (HPLC)/DAD/MSMS after derivatization with o-phenylendiamine to yield the quinoxaline derivative. Baseline separation of all α-dicarbonyl GDPs, particularly of the diastereomers 3-deoxyglucosone (3-DG) and 3-DGal, required the application of a polar, phenyl-based RP column for HPLC and additional pH-gradient elution. Concentrations of 3-DGal ranged between 55.8 and 136.9 μM in single-chamber PD fluids, and between 2.5 and 12.4 μM in double-chamber PD fluids. In solutions containing glucose, 3-DGal is formed from 3-DG via the intermediate 3,4-dideoxyglucosone-3-ene (3,4-DGE). Further studies are now required to determine the (patho-)physiological properties of 3-DGal.

3-deoxygalactosone, a "new" 1,2-dicarbonyl compound in milk products

1,2-Dicarbonyl compounds are formed in food during Maillard and caramelization reactions. 3-Deoxy-D-threo-hexos-2-ulose (3-deoxygalactosone, 3-DGal) and galactosone, two 1,2-dicarbonyl compounds originating from the degradation of galactose, were synthesized and converted to the respective quinoxalines, which were characterized by NMR spectroscopy. Analytical separation of the quinoxalines from the epimeric glucose-derived quinoxalines of 3-deoxyglucosone (3-DG) and glucosone was achieved by RP-HPLC on an RP-phenyl column. This method was used to study the relevance of galactose-derived 1,2-dicarbonyl compounds in a variety of foods. 3-DG and 3-DGal were quantified besides 3-deoxypentosone, methylglyoxal, and glyoxal after derivatization with o-phenylenediamine in lactose-hydrolyzed UHT milk, ranging from 2.5 to 18 mg/L and from 2.0 to 11 mg/L, respectively. The concentrations of both compounds tended to be higher in other lactose-hydrolyzed food items as well. During storage of lactose-hydrolyzed milk, the concentrations of the 3-deoxyhexosones first increased, but especially the concentration of 3-DGal tended to decrease on prolonged storage, pointing to lower stability of the compound. 3-DGal was also detected in galactose-free food items such as apple juice and beer. The possible formation of 3-DGal from 3-DG by 3,4-dideoxyglucosone-3-ene as an intermediate is discussed. Compared to the relatively high concentrations of 3-DG and 3-DGal, 3-deoxypentosone, methylglyoxal, and glyoxal were of only minor quantitative importance in all foods studied.

Identification and quantification of the glucose degradation product glucosone in peritoneal dialysis fluids by HPLC/DAD/MSMS

Glucose degradation products (GDPs) formed during heat sterilization of peritoneal dialysis (PD) fluids exert cytotoxic effects and promote the formation of advanced glycation end-products in the peritoneal cavity. As a result, long-term application of continuous ambulatory peritoneal dialysis is limited. The composition and concentration of GDPs in PD fluids must be known to evaluate their biological effects. The present study describes a targeted screening for novel GDPs in PD fluids. For this purpose, dicarbonyl compounds were converted with o-phenylenediamine to give the respective quinoxaline derivatives, which were selectively monitored by HPLC/diode array detector. Glucosone was thereby identified as a novel major GDP in PD fluids. Product identity was confirmed by LC/MSMS analysis using independently synthesized glucosone as a reference compound. Furthermore, a method was developed to quantify glucosone in PD fluids by HPLC/UV after derivatization with o-phenylenediamine. The method's limit of detection was 0.6 microM and the limit of quantitation 1.1 microM. A linear calibration curve was obtained between 1.1 and 113.9 microM (R(2)=0.9999). Analyzed at three different concentration levels, recovery varied between 95.6% and 102.0%. The coefficient of variation ranged between 0.4% and 4.7%. The method was then applied to the measurement of glucosone in typical PD fluids. Glucosone levels in double chamber bag PD fluids varied between not detectable and 6.7 microM. In single chamber bag fluids, glucosone levels ranged between 28.7 and 40.7 microM.

Profiling of alpha-dicarbonyl content of commercial honeys from different botanical origins: identification of 3,4-dideoxyglucoson-3-ene (3,4-DGE) and related compounds

The alpha-dicarbonyl contents of commercial honey samples from different botanical origins were analyzed as their quinoxaline derivatives using HPLC-DAD, HPLC-MS, HPLC-MS/MS, and HPLC-TOF-MS. A total of nine such compounds were detected, of which five were previously reported in honey (glucosone, 3-deoxyglucosone, glyoxal, methylglyoxal, and 2,3-butanedione) and three were reported only from sources other than honey [3-deoxypentulose, 1,4-dideoxyhexulose, and 3,4-dideoxyglucoson-3-ene (3,4-DGE)]. An unknown alpha-dicarbonyl compound was also tentatively identified as an oxidation product of 3,4-DGE and was termed 3,4-dideoxyglucosone-3,5-diene (3,4-DGD). Only glyoxal (0.3-1.3 mg/kg), methylglyoxal (0.8-33 mg/kg), and 2,3-butanedione (0-4.3 mg/kg) were quantified in all honey samples. Furthermore, analysis of the alpha-dicarbonyl profile of various honey samples indicated that certain alpha-dicarbonyl compounds are found in specific honey samples in much higher proportions relative to the average amounts. The free radical scavenging activity as measured by DPPH method has also indicated that the darker honey samples such as buckwheat, manuka, blueberry, and eucalyptus had higher antioxidant properties compared to lighter-colored samples.